Need help understanding amplifers

My question is about 2-channel amplifers. my reciever is a Onkyo 787 it requires an amplifer to get 7.1 sound for the side channels...My question is what should I look for in power and of course cost. I do not have super high end equipment , I am running what I can afford. My speakers are all the cambridge soundworks top of the line and I have 6.1 now I think I need a class in amplifer 101!!....Thanx for any help in this matter
You really do not need a lot of power to run the side channels in your setup. Anywhere from 35 to 100 watts per channel should be more than enough. At price points there are many to choose from but for low cost and good quality the Adcom or Parasound Halo amps are good and great choices for your needs. The Halo would be a better choice and offers more upgrade for the future like XLR inputs and adjustable gain per channel. It has been seen on this site for 500-600 with an 800 retail. The Adcoms run as low as 150 used. The Marantz slimline monoblocks are also a good choice here.
Thanx LJGI for your help, I will surely take your advice. It's hard to find help when everybody I ask is trying to sell me something , and of course what they have is the best choice. The Adcom was recomended more than once and I think the Marantz monoblocks are easy to find at a decent price...thanx again