After some additional research and a call to Klipsch, I was told to stay within 80% to 100% of the front speaker rating.
Since there is a limited offering of 7.2 channel AVR's that pump out 120 to 150 WPC,
I chose to buy a Marantz SR5011 and an external amp, Emotiva BasX A-300, to power the R-28F's.
Hope to have it all set up and fine tuned by this weekend.