I'm a bit new to Amps and other High End power sources. Could someone help me understand the need for a preamp? Also, most amps that I've seen rarely push more than 75-100 watts, but there are speakers that take 250. I understand the whole (twice the watts doesn't = twice the SPLs) Is there a good FAQ on Separates, Amps, and PreAmps; if not, could someone just speak on the issue a bit. Thanks!