I ended up using Euterpea, which in turn uses both Codec.Midi and Sound.PortMidi. My working environment was to have my code loaded up in ghci, play MIDI into a software MIDI bus, and pipe that into MainStage 3 which ran the synths.

The piece I was working on premiered last night at a concert in Wellington, NZ. The live recording will take a while, but you can hear a studio synth recording (from the above setup) here:

The code for the piece is all open source: https://github.com/mzero/PlainChanges2. In particular, there is a somewhat improved MIDI player in there.

Enjoy!

- Mark

P.S.: Yes, and now that that's done with, I can get on with the next Haskell Platform release!