Yep, the XMPlay MIDI plugin has finally appeared. It's a softsynth (ie. doesn't use MIDI hardware), and uses SF2 soundfonts. It's setup to use the Creative/Soundblaster soundfont by default, but any of the many SF2 soundfonts freely available on the 'net can be used (in the plugin config).
MIDI format 0 and format 1 files are supported, and the MIDI implementation supports all the main stuff, including the following events... note on, note off, key aftertouch, pitch bend, pitch bend range, patch/preset, bank select, tempo, volume, pan, modulation, expression, sustain/hold, reset all controllers, all notes off, all sound off.
The SF2 implementation is fairly complete, including support for multi-layered multi-region instruments, the volume and modulation envelopes, and the modulation and vibrato LFOs. It doesn't currently support the low-pass filter, but I may add that.
You'll probably want to enable the reverb to add a bit of extra depth to the sound. I may also add support for the MOD "surround sound" options.
Anyway, to get you started, here's a small (relatively) SF2 soundfont, with some nice example MIDIs included...
Now available on the XMPlay page.