I guess the problem is probably that a2dp could be added in and used out of the box (using Bluez-utils, or the DSP task), but.... Afaik, mixing is carried out in the DSP, and unfortunately there's no way of sharing data on the DSP, or returning it to the ARM (atm the mp3 decoders include a sink, as does the pcm-sink).

Without a way of seperating out the decoding/encoding/sink operations, there's not much hope of being able to re-direct system sounds as well as everything else, using the low-power DSP tasks.

It is not hard to get a2dp working in the short-term, but my feeling is that Nokia won't support it out of the box until there's a way of chaining DSP tasks (OpenMAX, which is where they are heading) to ensure that all audio output can be sent to the headset, and that decoding/encoding can be done in a power-optimal fashion (i.e. using the DSP).