The receiver is a combo pre/pro and amp all in one box. It typically has all the capabilities to corral all the inputs and direct outputs to speakers and display devices such as a TV or projector. Some of us like the flexibility of a separate amp so we can upgrade power occasionally. Also most recievers output power is less than what you can get for a dedicated amplifier. Typically recievers generally don't exceed 150 watts per channel output and that is about the limit because they need to keep all the parts cool. A separate amp allows us a far wider choice of what speakers we choose to power because amplifiers are available in all kinds of wattages from 10 to 1000s of watts. A lot of receivers have the capability to isolate their amp section from the pre/pro section to allow use of an outboard amp. For advice just google home theater and a bunch of online magazines will be found. Also try AVSforum.com