The easiest way to get surround sound in a 12v format is to uses a DVD
Receiver. Most of the mid and high range DVD
units come with surround sound built in. These units will play DVD's encoded with 5.1 surround sound. To get true surround sound emulation for non encoded audio, you'll also require independent amplifiers for each each channel (Front, Rear, Center, & Subwoofer) as well as crossovers for each channel, which will let you independently set the gain for each channel.
Here is a "factory" surround sound receiver that was car model specific.
2005 Acura TL Surround sound head
unit (The go for about $350)
I'm On point, On task, On message, and Off drugs. A Streetwise Smart Bomb, Out of rehab and In denial. Over the Top, On the edge, Under the Radar, and In Control. Behind the 8 ball, Ahead of the Curve and I've got a Love Child who sends me Hate mail. - (George Carlin)