I've been going through a whole load of old backup CD's I have, trying to have a little clear out, and I've finally found the old source to Ballistix! It looks pretty complete including editor and game code. However I'm not excited about that so much as the music player source I'd lost!
This was based on the HiredGuns octamed player (I think) and allows the full 6 channels to be used. It was attached to the timer IRQ which means I can probably plug it into virtually anything I do - particually since I also have the PC Engine music itself!
The music player was built ontop of my sound effects player which simulates the C64 ADSR stuff (since each channel had its own volume). There also appears to be a sample player (including a function called PlayAmigaSample) although I can't remember Ballistix playing samples at all... I'll need to hook it up again and have a listen...
It will also remind me how to arrange the ROM so that it'll actually load in an emultor - exciting stuff this!