I have so far not managed to get any HDMI audio from my TV via R9 285.

I can get HDMI sound when connected to a monitor (with cpu load)

With other h/w this TV has recently been OK with a bit of messing around eg.
extra run of xrandr + cpu load for R9 270x. RS880 and rv770 worked without the
cpu load.

Added complication since getting a new mobo I sometimes get i2c edid read fails
on the TV - but then it's not always and the rv770 produced them and worked and
the tonga always works for sound with the TV in windows.

I noticed that for the TV the eld does not match what edid decode reports - it
only shows one sample rate and shows "Fl/Fr C" when it's only 2 channel. TBH I
don't know what eld said historically with different h/w.

edid-decode and eld for TV attached.