The frameworks (SndKit, MusicKit) have been exercised fairly extensively and are quite stable.
MIDI recording and playback of scores and computed parts works on all supported platforms. The application ScorePlayer, the examples MidiFilePlayback and playscorefilemidi, and the utility playscore demonstrate these capabilities.
Sound recording and playback is also stable. The applications Spectro and TwoWaves, and the commands playsnd, recsnd demonstrate Sound recording/performance.