Stick with 5.1.
There are lots of speakers in that price range, and some sound similar and some sound different and some are VERY different from each other. Definitive Technology have a slightly "bright" sound to me but not irritating whereas Klipsch has a kind of in-your-face midrange and then Infinity's Primus series is on the "warm" side which means higher frequencies are softer and easier on the ears for some people. Everyone hears differently so you need to go out and listen before choosing. Try to bring your own music! It would be agood idea to burn a CD-R for that reason with different tracks from different albums because most retailers have crap demo music, if they have any at all. And dont allow them to use the radio, one of the worst sources of music for demos!*
Using music you are familiar with, even if it is not an audiophile quality recording, allows you to judge speakers better because at least you have some frame of reference based on your car system, your PC speakers, your headphones etc.
If you go out and demo, make sure the receiver is set up correctly a nd that means bass and treble set to "0", any DSP selections like hall, club or Dolby Pro-Logic IIx is turned off, or anything else that is adding artificial effects to the music. And if they demo with a sub turned on, try to make sure the receiver's bass management system is turned on so that if the left and right speakers, the "satellites", are very small they are NOT receiving a full range signal which could easily overdrive single 3" and 4" woofers, causing some ugly distortion. I see this all the time at big box stores.
Personally speaking I would stay away from those tiny satellites with 3 or 4 inch woofers especially with that powerful receiver, and stick with something with at least a 5 inch driver. I believe they are easier to blend with a subwoofer and the complete system just sounds fuller and more realsitic to me.
* I have been toying with the idea of using a flashdrive with 320k MP3 files for demo use, but not sure about plugging a piece of my own hardware into a demo unit that may have not been treated well. Plus trying to use the USB onscreen operating interface of a receiver I've probably never seen before could be a huge headache.