I have been away from this project for some time now. Had some fun coding a ZX81 demo :D
My immediate plan for SkajNätt is to make a sound-expansion card using an AVR as a DDS (Direct Digital Synthesis) chip with stereo output. 8 channels of simple waveforms and noise, ADSR, volume and pan per channel. Hopefully an analogue filter bank as well. Perhaps some rudimentary player built into the chip.
I've coded such things before, but not for the AVR. It'll be interesting to see how many of my goals I can reach with this.