It seems like you have quite the collection! I have a couple of eMacs that are sitting in my studio running OSX 10.3.9 currently and I have not even begun to get these to connect with anything else as of yet. I know they have potential even if they have small hard drives. If you manage to get all of your gear connected, that will be quite an accomplishment. You are not the only one with more gear than you know what to do with. Good luck.

Sounds like a lot of fun! I haven't built a system with that many nodes yet, so I may not know all the details or intricacies involved and/or sought after. Although, I have found this MIDI router that is expandable to suit the number of connections needed, specifically the MIDIX-HD (although the article is based around the MIDIX) Hinton Instruments MIDIX/MIDIX-HD. I didn't see any prices on their site, I think you would need to contact Hinton Instruments for more info, although there is a "view cart" button on the page in that link. Motu also makes a MIDI router, though it is an 8inx8out 1u unit MIDI Router. One would want to find a Rack to mount those units in, I think audio gear is typically has a form factor of 19" wide (there are other form-factors, one is 23", and the other is smaller, with the audio units mounting vertical instead of horizontal - I just didn't find it again). The MIDIX/MIDIX-HD uses an RS232 port to connect to a computer, where the MIDI Express XT uses USB. You could probably find a RS232 PCI-X/PCI card for your computer if you don't have one on your Motherboard/Logic-board (although I would definitely make sure to talk to Hinton Instruments about that.;) )

I was thinking, the Hinton Instruments MIDIX/MIDIX-HD is a 6u unit: the MIDI Express XT is a 1u. Seems like you would need 5 MIDI Express XT to between 5u - 10u needed depending on how you mount them. I wouldn't want to use all those USB ports on my computer, so I'd imagine that something kinda like this would help - USB to Thunderbolt2 dock. The reason why I would want thunderbolt is because it is much faster than USB 2, so the competition for bandwidth wouldn't restrict performance (bottleneck). I am not sure though, because I don't know how much MIDI data you will be sending, so I suppose it may be possible to get away with a USB to USB hub. I just did a quick google search, and there are pcie/pci-x thunderbolt 2 cards out there.

A quick read and comparison between these two showed me that they are "different" in what they do (or at least in what their product pages are showing about themselves). I suppose it may possible that they are the same or very similar for what you need/may-need.

I just thought that I'd add that Hinton Instruments web-site shows that they build custom MIDI solutions. Sometimes I think if I'd ever want to have something custom built, I'd try to find others who would buy the same thing I would, and order a few at the "same" time, perhaps creating the chance for a volume-discount (I don't know though, most likely depends on how many units or how many features of the custom build are needed, who knows, might be worth a shot).

I still use an old JL Cooper "SYNAPSE" with my MIDI gear, but I'm afraid it isn't a better solution for you. It is a stand alone device that has 16 MIDI ins and 20 MIDI outs with the ability to merge any 3 inputs at one time. It has some other MIDI processing capabilities as well. I also used to have an Anatek MIDI Studio Merge- it merges 8 inputs to one output- came in very handy when I wanted to do data dumps from certain units into my computer, I just plugged it into my SYNAPSE and used up only one input for 8 devices (the merge device would strip MIDI clock, so don't plug workstations into the merge box). There is now a company called MIDI Solutions that has a very similar device available.

I hope this helps.

Thank you Garrett and Steve. I was not aware of Hinton Instruments. Interesting design. It looks to me like it would work as a patchbay but I'm not sure it would work as an interface. It sounds like the RS232 connection is for configuring the routing not for actually passing MIDI from a DAW. Plus it would be quite expensive: they have an old MIDIX16 for sale on the website which they say is on special and is an ex-demo unit but they still want 1250 pounds for it! They may be interesting to talk to for a custom design as a last resort though but they wouldn't be cheap.
The MOTU MIDI Express XT would work nicely as an interface. As you pointed out I'd need several. I'd need to find out how a DAW handles multiple identical interfaces plugged into the computer. The downside there is that they wouldn't work that well as standalone patchbays when the computer is turned off. Each can be configured as a patchbay however I'm not sure they would be able to communicate with each other - for example to have a controller plugged into one XT play a module plugged into another XT. I guess sacrificing one pair of MIDI input/outputs on each XT for communication between patchbays could work, together with clever patching to minimize inter-patchbay connections.
The SYNAPSE also looks good as a patchbay but not as an interface. And it has the same problem as the Studio 5's: old and impossible to find replacements!

One solution I'm thinking about at the moment is using multiple iConnectMIDI4+ interfaces together with an old iDevice for processing and controlling. I have one iConnectMIDI4+ and it works nicely as an interface. In my DAW I can have up to 16 MIDI ports that can be routed in the iCM4+ to 4 MIDI DIN ports plus 8 ports off the USB Host socket plus 4 ports on the Ethernet/rtpMIDI link. So in principle it could work as a 16 in/out interface plus configurable standalone patchbay (with full MIDI merging capabilities) but I'd need to have 8 devices connected through USB MIDI. I do have a number of synths that accept USB MIDI, and a cheap class-compliant USB-MIDI converter could work to increase the number of DIN ports: I have tested something like this and it worked - although not sure of latency. It would also need 4 devices connected through the rtpMIDI/Ethernet port, and that's harder to do as the only rtpMIDI to DIN converters I could find are the Kissbox ones and they are rather expensive.

But it's still not enough ports so I'd need to get at least a second iConnectMIDI4+ plugged into the computer as well. Then I could use the Ethernet/rtpMIDI port to connect the two iConnectMIDI4+ together to allow cross-interface communication when the computer is off, and it would still give me 8 MIDI DIN ports plus 16 USB MIDI ports that could be addressed directly from the DAW as well as routed internally in standalone mode. That's 24 ports to play with, and some of these ports can be shared between multiple monotimbral synth modules that only require one MIDI channel (so for example I can have 8 synths on one port using an 8 output MIDI thru box). The iConnectMIDI4+ iConfig app is pretty involved and allows lots of routing and MIDI processing (filtering and channel remapping) but the interface can be arcane, it doesn't allow saving and switching configurations internally, and changing configurations on the fly is difficult. The iCM4+ can also be plugged into one or more iPhones/iPads which can provide some processing. I have experimented with plugging an ancient iPhone 4 into mine, running the Midibridge app, and that worked quite well for simple MIDI processing.

But I haven't been able to get an answer from iConnectivity yet as to whether multiple iCM4+ plugged into one PC are recognised properly and the type of latency I would get. I'm also not clear as to whether I'd be able to use the rtpMIDI ports for communication, or if there are better alternatives to the Kissbox converters (a third iCM4+ could actually work for that but it's getting a bit expensive for an extra 4 ports).

Another MIDI patchbay option I have come across is the MIDIbox MIDI matrix. Rather impressive specs - up to 56 ins and 56 outs. But it's only for patching/routing as far as I can tell - the 56 ports are not directly accessible from a DAW. And there's no MIDI processing or merging available. And it sounds like you need to build it yourself!

"I'd need to find out how a DAW handles multiple identical interfaces plugged into the computer" ASIO4ALL. that program make a bunch of stuff possible. I don't know if everything talks to it, but they should be able to

Just an addition, I haven't plugged on those MIDI routers in and see how ASIO4ALL handles it. My context for interfaces was transparent.

I meant, I haven't plugged in, not plugged on

Does ASIO4ALL do something special for MIDI? I thought it was only for audio interfaces

I don't know if ASIO4ALL is supposed to do that. I am thinking that the way ASIO4ALL works (what little I know of it) would be beneficial "in analogy" in this application for MIDI routers. I guess ASIO4ALL is just a clue or hint.

I am used to the automation of TCP/IP packet switching routers. I'd have to look into whether those MIDI routers have something similar.

With that amount of namespace (40 MIDI talking electronics), understanding how the central "switchboard" keeps track of each instance/entity ... just thinking aloud.

I don't know if this helps, but after reading through your post, I was reminded of a fact I experienced in my gear/rig: Nonnoticable audio output didn't sound good when attempting to output 8 channels of audio between two usb audio computer interfaces. When I used an interface that had 8 output channels, it sounded good. This is pretty much after MIDI in the process-chain, but could be indicative of something.