So you're using the center and sub from the HD500 set? There's a consideration of trying to have a match for the L/R mains to the center. Not sure what in the Klipsch lineup mates well with those speakers but you should be able to search for some help on that.
The fronts at only $400 a pair are going to offer limited options but perhaps a set of Ascend 200SEs or 170SEs (for a L/C/R setup that is) even with an increase in cost may be well worth the investment. Yes, I am an Ascend owner...200SEs and Sierra-1s. Good company to deal with and I think a great product for the price.
Next I'd consider upgrading that sub...a real sub can do wonders even with satellite type speakers...
ps I've also been very impressed with my Cambridge S-30's, good bang for the buck. Heard nice things about the Pioneer Andrew Jones-designed speakers (BS 41's?).