You could go a couple different ways. You could do a PPI P900.4 and run 4 speakers on the front channels and the sub on the rear channels bridged:
http://www.electotronics.com/precisi...w4channel.aspx
That would give a total of 450 watts RMS for your sub and 450 watts for the remaining 4 speakers (running at 2 ohms, so you'd have a pair on each of the channels)
Or you could do the PPI P900.5 which is a 5 channel amp.
http://www.rakuten.com/prod/precisio...P1EaAmVZ8P8HAQ
You'd have 70watts for each of the 4 speakers (280 total) and they'd be at 4 ohms. then you'd have 270watts for your sub (assuming it's 4 ohms) or 440 watts if it's 2 ohms.
Pretty similar either way as far as how much power gets to your speakers. so I'd say that you might be best going with the 5 channel because that would get you a bass knob to control the level of the subwoofer independently, and you'd be able to adjust/fade the level of each pair of DB651's independent of the other pair.