I'd be inclined to go with 2 EP 500s for the flatter response throughout the seating area.
Yes that's the move I'm gravitating towards as well. Having googled the EP800 it sounds very tempting, but I think two 500 watt ported subs will out perform a 1000 watt sealed subwoofer. Sure the sealed box can deliver lower bass, but I'm thinking that the 19 hz that the EP500's go down to will be sufficient. And the ported design will ultimately move more air.
Now I'm wondering if two main towers will be enough? I'm running my system with a Denon AVR-4802 reciever that will push the center channel with 150 watts, and all 6 surrounds (the 4802 is a 7.1 channel reciever that splits the 2 rear channels up to give you the option of running 4 rears, 2 sides as well as the center & fronts... It sounds amazing!) At 150 watts per channel. To push the left and right center speakers I have a Denon PMA-2000 on the way that will send 165 watts at 4 ohms to the M80's.
The speakers I have now are Cambridge Soundworks in the rear and Cerwin Vega's up front with a 220 watt Cerwin Vega down firing sub, and it sounds really awesome. So I'm almost wondering if 1000 watts worth of bass is going to drown out the 330 watts coming out of the front main speakers? From everything I've read about them they play exceptionally loud though, so I guess we'll see.
I just wish there was a local dealer around here... I'd LOVE to give that EP800 a listen!