I was looking at a Kicker zx350.4 amp and it has different input sensitivities for high level and low level. How do I know which I'm using? I'm basically a n00b with this though I used to have a PG x100.4 before it was stolen. I may grab another again but I'm looking at some other amps too. Also, the input sensitivity relates to the preout voltage on the head unit right? I just wanted to make sure. Thanks in advance.