Not sure about the Audio/Video switch, I don't believe my EP350 as one? In regards to the phase switch, this switch adjusts so your subs driver is in phase/out of phase with your l/r mains. Most people don't hear a difference, but it is my understanding you want them moving in/out at the same time. I found some music with a lot of low end frequencies, and played it with the switch in one position, then backed up to the beginning and switched to the other setting. You will notice the difference. I have my volume set at 12 o'clock and my receiver crossover at 80hz, and my sub crossover turned clockwise all the way to get it out of the way.
good luck
