Hello,
The problem here is that 'standard' midi assumes that all percussion is using a specific channel, and the 'instrument' is a 'drum kit', although you may be able to select different drum kits (as different instruments). Within the drum kit selected, different types of percussion are assigned to different note numbers.
What you describe sounds like it's set up to work within the same parameters, and that's all.
To do what you want to do, you'd need to be able to assign different channels to different pads, and then your external equipment could set the different channels to the instruments you require, but then you might not have any control over the actual note played, this may have to be fixed. I assume the 'pad' would supply note ON only, it may not even supply any note OFF?
An alternative might be an expensive type of synthesizer (there might be 'virtual' types that do the same thing) where the system is designed to have each note of a 'voice' to be separately sampled, and hence as each key is pressed the relevant sample is played. The design assumes that each sample is of the same instrument, but in fact they could be of different things, which would allow you to do what you want so that the pads would be assigned to a single channel,which would be attached to this device and then specific pads could be assigned to specific note numbers which would play the sounds you require.
There was a thread here a while back, which was headed towards a similar conclusion, and someone else suggested that there WAS such a device. I'll do some digging and see if I can spot it.
In any case, any solution may be dependant on a second device (or software) and may still need the controller you have, so there may be no point is selling it until you've got a complete solution worked out.
Aha, the thread I was thinking of has been recently revived,and is here:
https://www.midi.org/forum/959-midi-interface-for-samples
- is anything there of any help?
Geoff