I was at circuit city the other day and the salesperson said that ideally, if I wanted to run two speakers and a sub from an amp, I should buy two and have each seperate. Is this just their bullshit way of saying "spend more money"?

I'm looking at 4 channel amps, is it possible to run two speakers plus a sub off it, or do I need more channels?

initially I'd like more power for my speakers, I'm running a 40w headunit and 180w 4 way pioneers in the back, but I'm sure I'm not even getting 20w out of each speaker. I've heard about 40x4 watts actually meaning 15wx4 or something, so what would be the most cost effective way to get louder, and at higher quality - A new (higher watt) head unit, or an amp?

I'm passing on a sub for now, but back to the first question, would I need to buy a second amp when the time comes for the sub?

Suggested name brands along with info is appreciated.