Clemens ~ thank you so much for your interest & input. I have, in fact, tried exactly what you've suggested -- it's pretty well what was written on p. 256 of the manual. So, I've gone over everything for the umpteenth time:
First, I double checked the Setting on GB (Preferences > Audio > MIDI) -- I even unplugged the USB, re-plugged it, & physically viewed the "MIDI Status: 1 MIDI Input detected" go from "0" to "1". So again, I'm confident that we're good on the GB connections.
Next, on the MR 76 I hit Sound Select > MIDI-OUT: CH01 000:000 (see pic) . . . at this point it gets conflicting. I'm to "change the MIDI Channel to match the 'track' you are sending it to" . . . hitting the "Send to Track" button on the MR sends this "CH01 000:000" to any of the selected 16 Tracks ON the keyboard rather than the New Track IN GB. I simply select the Track #/button & hit "Enter", but then nothing appears or happens -- that is, NO SOUND from either keyboard or GB.
And yes, I checked ALL connections & volume levels, I tried putting on headphones, + no wave forms appear if I hit Record.
So . . . I cannot help but believe we are so very close, & that maybe the Operator (me) is missing just one very simple step. I've randomly changed every parameter, but no go.
The last line in your guidance also has me rather baffled: "Any track that has the MIDI Out instrument assigned to it will control any external MIDI module or keyboard connected." Hmmm . . .
One other thing: so you know it's just not me, I took the MR to Guitar Center & 2 different techs (both into recording themselves) were also stymied. We all got to the same point as in the pic, but couldn't make a 'sound'.
Have you any more rabbits in your hat? . . . thanks again, RnB