adlibtracker 2 has midi capability but i was never able to get it to work with my setup. from what i remember you would just be passing note data though, not instrument parameters.
It sounds like it may do what I want. I thought AT2 didn't support midi in. Passing note data would be enough as long as I can set up patches to be controlled by the midi input.
You may want to look at Frequency Monster 801 http://fm801.kewl.org/app/about/
It does most of what you asked about, but bad news is it only works with certain soundcards (ones based on the Yamaha YMF72x-74x PCI chip or clones). I opened a thread here about setting it up, on XP and it also runs on Win98.
Aside from the Yamaha soundcards with the chip there are 'No Names' like Labways or Aopen PCI cards that are usable, and very cheap on EBay.
Yogi
This sounds like a good option. I'm not familiar with the YMF7xx chips. Are they in some sound cards along side the OPL3, or do they replace the OPL? On Frequency Monster's site, I only see the requirement that it's an OPL3 compatible card and they list the SB16 and SBPro in their compatibility table. I'm not sure what's in the computer I have in mind for this. I think it's a Soundblaster 16 but I'm not sure yet. Also, is FM801 multitimbral? It looks like you may be limited to bitimbrality but it's not clear to me.
Dan
I also have sampled loops from AT2 and put them in Impulse Tracker, which is even more difficult because you have to figure out what is close in "tempo" pertaining to how each tracker calculates time.