Which of the values in the .ini file controls the music volume? I'm wanting to turn the music volume down a bit, and I'd rather not do it through the game settings menu from within the game as that will over-write other tweaks I've made to the .ini file.

Under the [AudioMenu] I see:
fAudioMasterVolume=3.0000
fVal7=1.0000
uID7=0
fVal6=1.0000
uID6=0
fVal5=1.0000
uID5=0
fVal4=1.0000
uID4=0
fVal3=1.0000
uID3=94881
fVal2=0.4000
uID2=466532
fVal1=1.0000
uID1=554685
fVal0=0.8500
uID0=1007612

Does anyone know which one of those control music volume?

Hi, if you're a lucky guy, that this :
fAudioMasterVolume=3.0000
to
fAudioMasterVolume=2.0000
or 5.0000 6.0000 ... if you want to have a louder sound.

For me, that doesn't work, I barely hear the game at my max volume, I've to wait 2 weeks and hope that the patch will fix that...

That is the setting for the MASTER volume, which adjusts all of the different audio equally. There are separate adjustments for each element, such as voice, music, effects, footsteps, etc.

After a little experimenting, I found the music volume setting...

fVal2

For me, the music very often drowned out the dialog, so I had to turn it down.

Adjusting the master volume above 1.000 does nothing at all.