I recently found a 360 Systems MIDI Bass Pro for cheap and bought it. It's the "Rack" version of the "Desktop" MIDI Bass and It has 8 sounds on board.

The unit can be expanded by installing other sounds using EPROMs, it has 16 slots in total and only 5 of them are used by default.

I bought some additional EPROMs on Ebay, but apparently, they are only meant to work on the "Standard" MIDI Bass, not on the "Pro".
I Instaled the EPROMs but they are not recognized...I suppose eithre the EPROMs are not the correct type or the content of the EPROMs is not compatible with my model.

If you have any idea or solution to this please write me or use the comments section :-D. Thanks!