OK guys, thanks! I'm working ALL day today so I'll try to do some experiments with daisy chaining tomorrow. In the mean time, is it also possible to take the same aproach with the MIDI interface and create multiple inputs as well?
I've never seen one for the Amiga, nor elsewhere (but there are probably some nowadays for the modern PCs).
Generally, you use a MIDI MERGE box or a MIDI patch bay to achieve more than one input. Again, though, you can use MIDI THRU to daisy chain multiple controller devices, with the final connection going to the Amiga's MIDI IN.
But could you please explain what are you trying to achieve? If you merely want to control both a drum machine and a sound module, any keyboard on the input side (usually your MIDI controller keyboard) can usually control any instrument on the output side. Yes, the keys on the master control keyboard can be made to trigger drum sounds on an outboard drum machine that's attached via MIDI. One input keyboard can control any MIDI devece on the outboard side (even if there are dozens of instruments, drum machines, samplers, effects units, digital recording decks, lighting rigs, etc.), as long as those devices have a MIDI input. You usually never need to touch the outboard instruments.