I never got into composing (much), but I still fondly remember my Yamaha DB50XG daughterboard plugged to a SB16 MCD (ISA bus). Haven't heard another MIDI, softsynth or wavetable that sounds as good since. Unfortunately, my last computer with ISA slots was a PPro, and something changed between versions in PlayMidi[1] to where the drums didn't sound as awesome. Thankfully, I still have MP3's of MIDI playback on that board for some of my favorite songs.

[1] - http://sourceforge.net/projects/playmidi/