Not totally ignoring your initial post, I thought I'd share what I did in my travel trailer. When I added a new LCD TV, I routed the audio from that (NOT through the headphone jack) to the car stereo I had recently installed. I intentionally selected a stereo that had auxiliary audio inputs on the back just for this purpose. Since the stereo wasn't getting enough power through the OEM wiring to properly power the speakers, I also added car audio amps near those speakers and a self powered sub-woofer. My system now kind of reminds one of a teenager's $500 car with the $1200 sound system. :) It rocks pretty darned good!
Unit's like the one I previously referenced are very inexpensive and do a surprisingly good job.