XPA-5 overkill for my system?

May be your speakers not able to handle the high volume well. That is a pretty beefy receiver. Seems to me you have plenty of power and may need speakers to match.

A center with a built-in powered sub?! Get a passive center and all shall be right with the world.

I also run a DefTech set up (STS mains and CS-8060HD for center, Gem XL surrounds). Considering your speakers and your receiver, I don't think the amp would add much. The center is pretty efficient, and the most demanding frequencies (bass) are handled by the internal amp.

If you are not happy with the output, I'd look at either A) adjusting the setup (different X0over, bass management settings, checking the Audyssey calibration), or B) more powerful mains (the SM65's are not too much larger, and are much more capable, while still blending with your center). Option A is free and option B is in the same ball park as the amp, either/both will provide you a more significant upgrade than adding an outboard amp to your setup.

Raise the center to 80Hz to match the FL/FR speakers.

^^^
Expanding on that idea, if you are running out of juice, try crossing over at a higher frequency. Depending on your sub (FR,quality, and location), crossing over at 100hz or 120hz will take a sizable amount of stress off your mains. This could allow for your system to be played louder and clearer, with more bass, and again, for free.

Audyssey tests for the -3db point, but the receiver sets the crossover/speaker size and crossover points, even if these are not optimal. Chris K. of Audyssey makes a frequent point of telling people to ignore the small/large settings, and to try a crossover around 80hz. At the worst, it was only a few minutes of time (you won't need to rerun Audyssey, just change the settings in your AVR)

Even with my STS towers, I tend to crossover at 100hz to my subs.

I don't think that either the XPA-5 or XPA-3 would be overkill. I have an XPA-3 that I bought because my "receiver" was clipping and it solved the problem. My system has been totally redone since then and I use three Emo amps along with a different "pre-pro."

You are talking about these?



"
one 5.25-inch cast basket bass/midrange drivers coupled to one 5.25-inch pressure-driven planar low-frequency radiators
one 1-inch pure aluminum dome tweeter
"

And the subwoofer is?

If there really isn't a subwoofer adding a good subwoofer costing you the price of an Emotiva XPA-5 will give you the following significant advantages:

(1) Superior bass because it doesn't take a lot to overpower what you got now (not a heck of a lot!) in the lowest octave

(2) Superior midbass because offloading the low bass from your fronts will make your fronts sound that much cleaner.

(3) Much higher SPL before AVR clipping because you're wasting a lot of power trying to make your fronts do what God never intended them to do, which is make low bass.

Ever hear the one about what happens if you try to make a pig fly?

The pig never flies but you pi$$ it off! ;-)

That is what happens if you try to get good subwoofer bass out of a 5.25 inch driver, or even twelve of them.

Are those his speakers? Sorry I didn't research what the speakers were. Your right, apart from Exodus Acoustics Anarchy drivers, 5.25" drivers are unsuitable for anything lower than about 100Hz. If he's getting distortion its pretty certain its the speakers and not the amplification.