I've never heard the 750's, but I can tell you that I listen to my 550's with my dual SVS subs turned off for 2 channel music. The bass is just so tight and fast in these things. I'm sure the 750's are awesome too, but I have been blown away by the 550's.
Okay, I have now just priced the Rockets including FedEx shipping and insurance anywhere in the 48 states.
RSC-200 (shipped) - $450 Pair of RS-550’s without risers (shipped) – $725 Pair of RS-550’s with risers (shipped) - $825 Pair of RS-550’s with risers and RSC-200 center channel (shipped) - $1250