The power range of 500-600W RMS makes this tough. I see DD as their power rating for 608 published as a range from 300W - 600W. If you want a beefier 8 I believe I can do a pair of American Bass VFL8s in dual 4.
OP, take a look at the CT Sounds Hydro. They're around $75 each and I wouldn't hesitate to run 600-700w each (clean). They sound really clean, can handle a good bit of power, and mine had no problem playing down to the lower 20's.