I am trying to decide whether to replace my Optimus ProX77 speakersóused for rear surroundówith Polk S10 Signature Series surrounds. There's nothing really wrong with the Optimi...just considering an upgrade. That's the point. Would this in fact be an upgrade?

Front speakers are Axiom M2, IntAmp is Cambridge Audio Azur 540R V3. Sub is AR S112PS. It's all in a rather acoustically unfriendly spot in my unfinished but partly carpeted basement. It looks like I could squeeze a bit more mids and lows out of the Polks, as compared to the X77s. There would likely be a Return option on the Polks, so I could just get them and see what's what. But I thought I would ask for some opinion first. Surrounds with 4" mid/woofer is about as big as I want to go. Looking to keep things < 200 USD. Thanks.