YES, it's called a high-low converter. and you'd def. better get one if plan on using the stock headunit!!! unless your head unit has RCA outputs already. if you don't plan on buying a aftermarket headunit, get the converter. get a good converter and don't cheap out. i believe they make some that just hook up and some that require power, and i'd def. say get the ones that require power. and the some converters also come with switches where you are able to adjust the frequency levels. those are the best ones in my opinion. all you have to do is hook up a 14 or 16 gauge wire to it and take it right off the power source for the amp, unless you got a distribution block that you can use. and also, like mentioned already, i'd also install a switch. you're headunit should have a remote wire and that's where the switch goes. if you don't have the radio on, you don't want the amps on. the problem you've got is very simple and can be fixed in about an about an hour or less. i wouldn't take the car back to the shop, just do it yourself.