The problem is the usual cross-platform issues. OpenAL is quite powerful and should be usable for T2/T3 - and I assume is used at the moment by AGK.
A lot depends upon what you want to do with it. Complex mixing and pitch-shifting is fairly processor-intensive. However, I did it on CDTV and CD32 on slow processors by today's standards - but that was not with complex graphics operations going on.
If it's a simple case like Play This Sample At 480 Hz, that's not too bad. Getting seamless pitch changes for car engines is not trivial. I programmed all the interactive audio stuff for the London Transport Museum when it opened. In the Optare bus, you could simulate driving it. When you used the accelerator it had to "know" when the automatic gear would change, and then do the correct audio transition to the next ratio, without jumping or pops and clicks.
This looks possible in OpenAL, but I can't see it ever being easily possible in AppGameKit Basic. Play X at Y frequency could be implemented quite easily. For anything fancy you need low-level access to the audio buffers and very fast event callbacks or interrupts.
The simplest (!) way to do it would actually be using a Midi playback system. But - I've read the warnings - this is still going to eat CPU time.
If you're on Windows or a Mac, it's not too big a problem, but some plastic phone with a 1.5-bit processor is going to die!
-- Jim DO IT FASTER, EASIER AND BETTER WITH AppGameKit FOR PASCAL