I just purchased a pair of RTi6 (http://www.polkaudio.com/homeaudio/products/recent/rti6/) speakers for a great price but ran into a problem. They are a bit bulky for rears but they have great sound. My system features a pair of Mission 765i floor standing speakers but for center I have an Energy EC-100 (Review (http://www.audioreview.com/cat/speakers/center-channels/energy-loudspeakers/ec-100/PRD_119509_2743crx.aspx). In my opinion the weak point of my setup. So instead of replacing my rear speakers I though what if I put two of the RTi6 on their side and use them as center, I am already running a SP4 wire so that would be easy. What I am not sure is would a Ti6 work as a center, or have I gone insane?

Any opinion would be appreciated.

Besides impedance issues, using 2 speakers for your center speaker is a no-no. This creates some unwanted acoustic anomalies. You should use one speaker for your center speaker just as you use one speaker for every other channel.

Otherwise, there is no reason at all that an RTi6 can't be used as a center channel speaker. They work just fine as L/R speakers, don't they? One RTi6, used vertically, would work great but you are still going to have a timbre mismatch. But it may likely sound better than your current horizontal center channel speaker. Easy enough to try it. If you do not have room to use an RTi6 vertically, you could try it on its side. It should work quite well on its side, actually.

But your center speaker's placement and implementation may be affecting its performance more than anything. Do you have a picture of the front end of your setup?

...did not work. But there is space.