Looking at an H/K 520

Crebbs

My dad is looking to upgrade from an older technics receiver and I'm not sure how much exactly he's willing to spend but he expressed interest in the H/K 520 or maybe an Onkyo model. I was just wondering if the H/K would be enough power to run the system he's got. Right now he's got two big polk fronts, which are some older model with two mids, a tweeter and 1 active/1 passive sub in each. He's also going to upgade to some new polk surrounds, and a new center channel, and he just got the 450 sub. So like I said, would the 520 be enough power, because I think that's the model he's leaning towards right now. If it isn't, where should we look and what should we look for in an external amp if he still wants to get that receiver? Also, is it better to go with a center channel speaker as the center-rear channel speaker or should he get a regular surround speaker to go there? Thanks for the input...