Thank you Janost, this is exactly the kind of pointers i was hoping for.
I have been looking at Matt Sarnoff's 1-bit AVR "Nastysynth" for atmega48 and timer1.
Does this (in your audio coding experience) contain the kind of elements that I require for this task ? It looks like Matt is using the kind of 16-bit phaseaccumulators that you're talking about.
I still haven't looked at the code close enough to determine if he's using a 16-bit timer, in which case porting the code requires some extra work.
Could you explain the concept in just a teeny weeny little more detail ? I can figure out the pwm settings and such, but more the audio-specific implementation of phase accumulators and how they combine with the pwm ?