Surround Speaker Choice

[Toofy]

Looking for some advice on Surround speaker choices.

I currently have 2 Sierra 2EX's (mains), Polk S35 (center), and 1 Monolith 10inch THX subwoofer all powered by a Yamaha Rx V2085. I'm more into music but now starting to get more into home theatre/movies.

I currently love my Sierra 2EX's and was wondering if it is necessary that I should buy another 2 Sierra 2EX's for the right and left surrounds or would the much cheaper 340 CMT's(that I've heard are excellent for the price) do just as good a job for HT?

I've heard that surround speakers generally don't need to be as articulate as the mains. I'm still very new to the HT game, so any info is much appreciated.