I'm surprised you had problems with OctaMED, I've used it for MIDI sequencing for years.
Ensure that MIDI is enabled in the midi menu, then go to the instrument editor.
Pick a midi channel and set the transpose to around 36 (that's what I have to do for most GM patches), volume to 40 (hex) and set a non zero preset. Play a few notes, you should hear something at least.
Me too, I have used OctaMED SS just fine to play into the tracker ; or from the amiga keyboard, triggering the instrument's sounds.
I never had to do anything tricky, just set 'midi active' or 'input active'.
Ah, but you do need to set up Octamed instrument, set its volume up to 64, because by default it is set to 0. And set a channel, 1 is good for tests.
