Be gentle cause I'm a newbie. I have the RC-51 bookshelf speakers for my fronts and the RC-52 for my center. My girlfriend recently purchased for me the Synergy Quintet III system along with the Sub-10 subwoofer for a great price. Was wondering if it would sound ok to keep the quintet speakers and use them for my surrounds in a 7.1 system or trade them in for the RS-42 surrounds. Basically was wondering if it makes that much of a difference since it is just for surround sound. Also, will the Sub-10 be ok to use, or again, trade it in and get the RPW-10. Living in a condo now so I can't really turn them up that much now, but looking to get out soon and do't want to have to buy new equipment again. Thanks for any advice.

In 7.1, the rear surrounds get the least action.  I say hook them up and see how you like the sound.  Ifyou're not satisfied, then by all means, trade them in on the RS42's...........  Same thing for the sub.  If it's enough for your apartment, then use it, if not, upgrade! 

And welcome to the world of Klipsch!  This forum is great to obtain information from, so don't be shy; and there is no such thing as a dumb question on here!

Thanks for the response, I will check them out. Was just asking cause I will use them for side and rear surround. Also, if I were to get the RS-42, where do you recommend I place them: side or rear, and what other speakers would I use for the other remaining speakers. Hope I didnt confuse you. The subwoofer should be fine cause the one I have now is a small sony and it is good enough so I am assuming the the Sub-10 will be. Thanks again.

http://www.thx.com/home/setup/speakers/71.html

that will tell you all you need to know.  But they suggest bookshelf, or "straight firing" speakers for the rears.......

 Much appreciated. Thanks for all the help.

Most around here suggest to use wide dispersion (the RS series) for the side surrounds and direct firing speakers (RB and RF series) speakers for the back surrounds.  So if you picked up the RS-42's, the ideal placement is about 10 - 20 degrees behind the listening area on the side walls.

You are heading in the right direction.  Here are the recommended speakers for a 5.1 system using the RB-51's up front. Later down the road, if you wanted to upgrade your mains, you could move the RB-51's to rear duty and get a pair of RF-52's for the front to make a 7.1 system.

Welcome to the forums!