WinUAE also has Midi support. I know you want a tracker-type solution but OctaMED SoundStudio may need a lot of tweaking to work and might not work well. Older OctaMED versions do 8 channel Midi too and tend to be a bit snappier.
I'd also suggest taking a look at Music-X which combines Midi and Paula, Bars 'n' Pipes and Dr T's KCS.
This might come in handy.