We might have made some progress... With the driver provided in #1 and after adding missing ids, my AV receiver lights left and right front channels, before it used to print "No data". But still no sound, I tried with xmms, mplayer and speaker test. Same commands work with an ATI HD4350.
I've unmuted all digital output as you can see here:
I've tested with drivers 190.53 and 195.30.