Several months ago Sony released two DVD / SACD players for the car - but they have been poorly announced in general.
Perhaps the most important thing people are missing is that because these players are DVD players as well, almost ALL surround discs can be played. Not only surround (multichannel) SACDs, but any DVD-Video or DVD-Audio disc with a Dolby Digital or DTS surround mix can also be played, as well as the handful of DTS discs.
The only surround discs that cannot be played are "pure" DVD-Audio discs. I've got a handful of those, but the overwhelming majority of my surround material will play on my MEX-DV2000.
My Sony MEX-DV2000 is the 1 DIN unit and it can be had for the amazing price of $200 on the Internet. I have a 1 1/2 DIN dashboard, so I bought the Clarion SRK5 1/2 DIN center channel speaker (at last, the music and voices coming from my knees are gone!)
The 2-DIN unit is the Sony XAV-W1, which Crutchfield is carrying, no doubt because it's a DVD player. I have no personal experience with this unit. Obviouisly it's their premium model ($799 list) with a built-in video screen, but there is a negative if you don't have a slot left for the center channel.
I rounded out my system with an Infinity REF1220SE subwoofer (12" in a beautiful box) and a Sony slim series subwoofer amp, AND the Sony HD radio box (how they got all that junk up in the dashboard I don't know).
I LOVE having surround in the car, LOVE having a center channel speaker and enjoy the subwoofer as I'm an organ music lover. The HD Radio does sound better than regular FM - it seems that the subwoofer gets more signal from digital channels as well.
I do find I need to fiddle with the subwoofer level as the response curve of the overall system is all too obviously not flat; I also suspect that the crossover point between the main channels and the subwoofer channel are not handled well on some albums, but it's clearly exacerbated in the car.
Here's my list of center channel speakers (devilishly hard to find):
Car Center Channel speakers (updated 7/1/2007)
1) Clarion SRK5 - 1/2 DIN - with its own amplifier.
2) Kenwood KSC-510CTR (dashtop speaker with amplifier)
3) The Clarion 1/2 DIN unit seems to be identical to the Pyle PLVWCRK5 (also speaker and amplifier)
4) Pioneer TS-CX7 dashtop speaker ; no amplifier
5) Alpine SBS-05DC - 1 DIN in-dash speaker; no amplifier
The MEX-DV2000 is not perfect. The white backlighting around the rotary knob becomes the brightest thing in the car at night, and the "TUNER" option stil displays even thought the only radio signal is coming from the "HD" source, but all in all, I've never enjoyed music so much in the car (okay, with a 12" sub it's an SUV).
Finally, for those looking for more information on the 4,900 SACD releases to date, check out this excellent site: http://sa-cd.net