If you do in fact have upgraditis and must buy an amp

, I recommend buying a stereo amp for your front Left & Right speakers since all the power requirement is here (and in the Subwoofer).
Your center speaker only gets the dialogue and the surrounds only get the ambience effects, which is probably no more than 10 watts of power per channel.
Check out this beast -The ATI AT3002 amp:
The asking price is $1,400 + shipping. The retail price is $2,500.
http://www.audiogon.com/cgi-bin/cls.pl?ampsmult&1307911246
Classic Audio Parts is an Authorized ATI dealer, and this amp is in perfect 10/10 condition, which means it looks brand new and smells brand new.
You get the full 7 yrs parts and labor warranty (mail in registration card). They even give you a free trigger cable for auto-on.
It produces more than 300 watts per channel into 8 ohms, and close to 600 Watts per channel into 4 ohms.
ATI make amps for the likes of Mark Levinson, Lexicon, JBL, Outlaw Audio, and 1/2 dozen other companies. ATI also owns Theta Digital.
Unlike those Emotiva amps and most amps out there, this ATI amp is FULLY BALANCED from Input to Output. It also uses a "fuseless" technology, which means you will never have to worry about frying any fuses in your amp.