I have several older A/B car audio amplifiers and was hoping there is a way to determine if I can use a differential input signal? They have RCA connectors on the inputs. This video https://www.youtube.com/watch?v=QOagVDZLQnA popped up in a thread on a car audio forum and I was unsure if it was just as easy as he states. Not to mention different meters have different max levels of resistance for indicating continuity. The amplifiers I have measure 10k ohm between RCA input shield and the ground terminal.