Thankyou Polyphony, this feature is awesome!
Two things would make it even better:
I would like to be able to set a different playlist for Race, Replay and Menu's.
I find with my own BGM I have to set the volumes at 120 for the music and turn the Race Sound Effects down to about 50 before I can actually hear the music, some of those Race Cars are very loud, which is realistic, so it's all good.
So the second thing that would be handy is a volume preview, so you can hear how the engine noises are going to blend with the music as it takes ages to go back out of the options then back in to a race just to see if it's right.
Big thanks for supporting ATRAC, I ripped my entire music collection to the HDD when I first got my PS3, to save the poor Blu Ray drive, and finally GT5 supports them perfectly, with awesome 352 Kbps Sound quality!
Third wish would be for the PS3 to support some sort of lossless audio, but I guess that's asking a bit much, I still play my SACD's as they apparently sound better than ATRAC.