Hmmm... M80 ($1330) + EP500 ($1230) = $2560. It's ok if $560 over budget will work.

EP350 might work, but there's a lot of open space into the office and game room that would have to be added into the total sq footage mix.

I'm no expert, but it seems that the 500 watts versus 300 watts would make a big difference. Although, I suppose you could run a single EP350 now then add another one to the back of the room later.