I thought about this and I realised, that triggering with keyboard should work fine.
so.
It could be done this way:
RShoulder + down arrow on song screen should open this mapping screen for keyboard keys
you could change triggering key by doublepressing A button on nonempty chain
or (better) with directly tapping a keyboard key you'd like to use as trigger (in song play mode)
only keys mapped to normal piggy navigating buttons should't be selected here (it will work as expected - up, down, left, right, select, start, LShoulder, RShoulder ) depending on how this is mapped in config.xml (or default)
RShoulder + F1-F8 should work as mute / unmute channels 1-8
Trigger keys shoul work in live mode this way:
Trigger on nonplaying chain will work as START on nonplaying chain
Trigger + Trigger (hit twice) on nonplaying chain will work as START + START on nonplaying chain
RShoulder + Trigger will stop assigned chain (or RShoulder + Trigger + Trigger (twice))
So, what do you think about this?