I have a Planet Audio 5 channel amp Model P600.5S it has Hi Pass and Level for the mids and highs and Gain, Level, Bass boost, Frequency and Phase for the sub. I used the DD-1 and verified my maximum volume on the Pioneer Avic D-3 is 35 so I moved on to setting the gains and here is where my questions come in. I raise the levels on the front and rear channel until distortion is detected and backed off. Moved on to the sub woofer I found I could turn the gain all the way up and no distortion was detected. It wasn't until I turned the level and bass boost was distortion detected. I reconnected the speaker wires and turned it on and it doesn't sound very good. The sound is flat. (Yes, I did return my EQ and HPF back the way I had it.) The bass sounds like I need volume 35 before it hits and then the front and rear speakers are so loud. Before I messed with it, it sounded much better. I guess my question is what do you think the problem is? Why does the gain have no effect on the sub? What should the frequency be set to? What is the purpose of the gain and level?