Thanks for the answers !
Today I made a test for the first time : inputing the amiga inside my PC (linux) soundcard (line input), so I could mix it with internal software (thru Jack and Ardour, probably) and use my midi mixing controller.
I noticed that my amiga 1200 sound level (or gain?) is very loud. I have to put it almost at 0 in the audio settings, and even like this it still a lot louder than my soundcard output. Does every amiga "sounds" loud like this ?
Maybe a sound level option inside your software would be a nice feature, but I don't know if a lot of other people will need this, or if it will do the same on every sound card. I also didn't made fine tuning with a mixer software, so I just say what I first discovered plugin the amiga inside the soundcard.
Last thing, about the keyboard limitation : maybe the keyboard "matrix" would allow another key simultaneous combination ? I'm pretty sure that Function keys can be pushed simultaneously (I have to verify). Maybe you could swap the loop keys to 1-0 keys and put the trigger functions to the F1-f4 keys ?