From what I understand, car audio amps are designed to operate from a 12VDC power supply, which is why painttoad's buddy suggests driving amps with a bank of batteries (which provide DC power rather than AC). I did a little googling to try to find a little more info on exactly what all has to happen in a home theater amp, in order to help confirm some assumptions I was starting out with. First, there's the transformer, which is stepping the voltage down to a more manageable level. The output of this transformer is still going to be AC, though, so the car amp wouldn't be able to connect to it. You would still need a rectifier to provide DV voltage from the AC source. There are also some capacitors tucked in after the rectifier. The capacitors may be part of the car amps, but the transformer and rectifier are not - and the copper wire windings in a good transformer alone likely account for a significant portion of the difference in cost between car and home amps.

I guess the bottom line is that a big beefy transformer alone cannot allow a car amp to be plugged into a 120V wall outlet. The power supply package required to do this can be scratch built by someone with some electrical know-how, but it's not likely to be a straightforward process. The simplest route from an installation standpoint certainly sounds like it is to borrow the car audio shop approach of banks of 12V batteries that you charge when not using the system, but there's a hassle factor there. Having seen the code-mandated ventilation requirements for commercial buildings with lead-acid battery banks located inside, I also wonder about what hazards (both fire and health) might be involved in bringing a group of such batteries into the living room on a permanent basis. As tekdredger noted earlier in the thread, these batteries can produce noxious gases. Building a power supply that outputs clean 12V DC would be the surest and most convenient way to drive a car amp from house power, but there are two factors that make me tend to recommend against it for anything except experimentation. First, the cost involved in buying or building such a power supply is going to probably wipe out the money saved from buying the car amp. Second, when you buy a home theater amp you are getting a power supply section designed by an electrical engineer specifically to power that amp, with a myriad of design decisions that you and I may not have any idea about - if we try to duplicate that design effort for a power supply to drive a car amp, the end result is likely to not be as good, and that could yield a system that colors or distorts the signal being sent to the speaker.