i was wondering if someone can please list the advantages and disadvantages of four channel amps and two channel amplifiers. i have the chance to buy a mad discounted jensen 4 channel 600 watt amplifier from a friend, but i wanted to know more about them first. i know four channel can amplify four speakers, and a two channel can only amplify two speakers - but, can an amplifier also amp up your sub woofer? or do you have to buy a mono ampilifier just for that? thanks in advance for any help, peace out.