Ok here's a new version of the patch, with a couple MIDI-related tweaks. It's now possible to override the default MIDI device and choose a specific device, using darkfix_setup.exe (there's also some display-related options there, but ignore them for now, they are disabled). Should be particularly useful for Windows 8 systems, given that the MIDI mapper is now gone.
Interestingly, overriding the default MIDI device solves the need to use Win95 compatibility in order to get MIDI music at all. In any case, you may want to keep Win95 compatibility for now anyway, as it may still provide a smoother gameplay. At least until i tweak a few P2 threading issues a bit. Your experience may vary, so try with and without Win95 compatibility and use whatever feels best.
P2 still does not work properly with VirtualMIDI Synth under Windows 7/8, but these changes ended up providing a few clues as to what may be wrong. Not sure if I can fix it easily, but we'll see… In any case, you should be able to make it work for now by explicitly choosing the Microsoft GS Wavetable on darkfix_setup.
PS: if you made any changes to DARK.FIX since installing the previous version of the patch, you may not want to overwrite it with the default version included in this zip.