Well, the driver now plays something a bit more sophisticated than crackles - it even sounds slightly like my daughter telling me I've got an email when I use my test sound.
But I still have lots of problems. it only plays on the left hand side for instance (a consequence of me not working out how to handle stereo in this model) and it get stuck in an endless loop. Previously - in the white noise era - it didn't, so it's been two steps forward and one step back in that regard.
The main breakthrough today has been on the ARM7 side - I dug up some arm7-elf generating tools (couldn't be bothered to build them all myself so got RPMs and installed them on a Fedora box I have here - my main dev box is Ubuntu these days). Wrote some new code to raise an interrupt - needed, I think, for the driver's overall health - and not only did this code work (the SH4 portion treats it as firmware), it played better sound - I think the only firmware may have been broken or corrupted over time.