I don't really know, I've never listened to them. Energy is a quality manufacturer, and I presume any high-end speaker they've made is a good unit. On a scale of 1 to 10, with 1 being a boombox and 10 being a $100,000 speaker, these are probably a solid 6, while those Polks you have are a 3.
The trouble is that you seem to be trying to build a multichannel setup with great mains and poor surrounds. I'm not sure how satisfying that would be. What other equipment do you have? Do you have a sub? What sort of place will you be using them?
Personally I'd be tempted to use them as dedicated music speakers in some other room by pairing them with a high quality stereo receiver and do something else for the HT.