Welcome to the forum
Don't go non-Klipsch. I would be on the lookout for a used KLF-C7 on E-bay or Audiogon.
I personally think an RC-7 (I wouldn't go lower) would suffice and sound great. If you go this route keep the box and packing material in pristine condition so you can take it back in case I am wrong.
If the RC-7 works out (and you can't find 2 more KLF 20's for side surrounds

) The RS-7's would be OK, but I prefer a direct radiating speaker over the WDST design (My Denon allows 2 sets of Side surrounds and what I would consider the ideal situation;-). If you don't like the match with the RC-7/KLF 20 combo, the RS-7's should still work as side surrounds.