Today I reverse engineered the driver for the Micronas audio chip and can now play MP3 files (only those are supported) with hardware acceleration. The CPU usage for playing an MP3 file with this driver is ~5% while the same MP3 file consumes ~19% when played with the Gizmondo music player. The driver also shows signs of MIDI support (another hardware/chip feature) but it doesn't work, probably not yet finished by the developers.
EDIT: The driver does support MIDI files but they have to be in a certain format.