just a few thoughts from my readings and experience regarding HT center channel speakers...
Center channel speakers are, in theory, designed more for voices and a wide dispersion pattern than anything else. The best really do a remarkable job of making voices sound natural and cover the entire listening area.. the worst over emphasized in the highs and are "beamy". All lack bass, unless they make it a point of having bass, powered or otherwise, but these are always large and expensive. The norm is they are designed to be used with subwoofers. The best still go no lower than 60 htz while most actually, like many little satellites, only go down to only 80 htz to 100 htz. I've tried four different speakers for a center in what is now my son's living room.... and even the B&W LCR3 sounds pretty poor. In the garage system I tried a single NHT SuperOne for the center channel... the SuperOne are known for good voicing, but ended up having to use two... which itself proves troublesome.
The point here is that centers are usually not good all around speakers... no matter what they say in the specs or advertising.
I'd suggest a couple of things to consider and look at... the first being larger indoor/outdoor speakers... something like the KEF Ventura 5 would work very well in your application and are the right size, have a better dispersion pattern and go down to at least 60 htz .... or secondly NHT SuperOnes or possibly their newer siblings.. any that are rated to voice well. I have less than $50 into my SuperOnes including the wall mounts thanks to Craigslist! Maybe the small Advents? but if I remember correctly they were a bit beamy...