usually when my protection light would come on it meant there was a bad ground. moving the ground wire to a better location on your vehicle should work (at least for me it did lol)
yeah, if your home theater system does not have a headphone jack you can get an adapter for rca to 3.5mm jack and that should work. im not sure if it will have "true" 5.1 surround but i have my pc hooked up to my home theater via headphone jack and all of my 5.1 speakers work