I don't understand the RCA with a diff signal
If the Head Unit is putting out a diff signal with a typical RCA that would mean one of the signal pair is running on the shield . It the shields should touch in a cable bundle that would mean the outside signals are shorted to each other.
Is there a different kind of RCA for differential signals? How do the amp
manufacturers handle this?
If the first proposition is true and there is anyplace where jumped RCA's can touch then it looks like you should put some tape or some kind of insulator around them.