For the longest time I had decided that my instrument would stay tied to external synths for all audio output. At this point in time I think that I can change this. I'm not trying to add performance ready sound, but rather a way to practice without the need of an external synth.
VLSI's VS1053b can do real-time MIDI, MP3, and Ogg Vorbis decoding. It can be purchased in small quantities and is easily interfaced with a simple serial stream of MIDI data. It can handle headphone level amplification and can be turned off if not in use to preserve battery life.
The sound quality is similar to an early Sound Blaster card. It can also decode OGG and MP3. Power usage under payback and headphone amplification should be around 11mA, which is doable.
This will have to wait a few months until I'm back stateside, but I'm excited about the chance to add onboard audio to my project that is power and form friendly.
The following video has sample audio from the chip. breath data could be mapped to volume/expression to make it more responsive.