You basically have two options for the bedroom Sound System
One is to get another automotive unit, Places like Crutchfield: LCD TV, Car Stereo, Home Theater, Speakers, Plasma TV
can give you some ideas there, They have about the best selection to be had
Or you can go with something like a BOOM BOX.. I have a uint, sold under many names mine is Memorex.. It happens it runs on 12vac provided by a standard "Brick" type power cord
Just unplug the cord, get the proper 12 volt accessory cord at Radio Shack and plug in to any handy 12volt outlet
I added 3 of those in the bedroom.
Runs on batteries too as I recall.