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?).
"I realize that somebody playing free music isn't as commercial as a hamburger stand. But is it because you can eat a hamburger and hold it in your hand and you can't do that with music? Is it too free to control?" - Don Van Vliet (aka Captain Beefheart) discussing commercial success in the music biz