This fiver has
A = Two Bedroom Speakers
B = Four Living Area Speakers
C = Two Outdoor Speakers
The "J" has buttons A, B, and C and the sets of speakers can be selected in any combination. I think the switch would solve the problem. Use it for say A and B on "Front" and then wire "C" to the rear.
I think what these folk plan to do is try and contact J, see if there's a re-furb program and at what price. If they do that, get lucky and the replacement lasts longer, the swap-out is simply plug and play.
Looked at some car stereo units and a few seemed to have the traditional three RCA jacks for video: Red, White, Yellow. If they want to go that way I think I'll suggest they call somebody like Crutchfield and talk about which unit covers the most features.
Might as well use a household DVD Player. TV itself is 120 VAC after all.