Seems this Thread has been not been that active, but hell, I might as well still add something interesting:
My father bought the (up to this day!) recent Audi A3 two years ago. It has the optional MMI-Touch Navigation System PLUS the Bang & Olufsen Surround Sound Speaker Set (totaling a shy 3.500€ :yikes ) which can at least play Dolby Digital (2.0, 4.0 and 5.1) and DTS (2.0, 4.0, 5.1) properly. SACD, DVD-A is NOT supported, and sadly DTS-CDs are not decoded, too.
For what I know, if anyone is interested in buying a luxurious German Automobile, every Audi (starting from the A1) in combination with either the Bose Sound System (which, I can't believe I'd ever say this, is surprisingly good) or the Bang & Olufsen Sound System PLUS the fat MMI Satellite Nav will give you at least lossy Dolby or DTS Surround Sound playback in a Car.
While it can also (surprisingly) play 192khz / 24 bit Stereo, it can not process the files properly when you give them WAVs in 5.1. It will just play back a Stereo downmix of the Source...
Mind you: You need both the fattest available Sat Nav and the big speaker set – or you'll be cut out of it...
And I have to say – even when the price is laughably steep – if I'd ever have that much money to spend on a car, I'd definitely buy the whole package. The Surround ambience from good masters (say the PF DSOTM in 5.1) is astonishingly good. Especially in a five door hot hatch.