I have the Denon AVR 4806 with the Audyssey MultiEQ XT room correction software. I also have a SVS PC Ultra sub. Would this product be overkill or would I benefit from something like this?

I'm not familiar enough with the Audyssey to know for certain. I will say that it's hard to find something that offers more capability for subwoofer equalization than the SMS-1. If you can set the Audyssey to leave the low frequencies alone, I'd say that it's worth a try.

Like any good room correction system, MultEQxt concentrates on correcting the low frequencies more than the rest of the frequency range.

A couple of advantages with the Audyssey: it correlates data from measurements at multiple locations, so you have a better chance of catching problems compared to measuring from only the sweet spot; it also measures in the time domain, looking not just for low frequencies that are louder but also for ones that linger in the room and have the longest decay times.

I would first try doing everything I could with the receiver's built-in room correction. If you're still not satisfied with the low frequency response in your room, then I would consider adding the SMS-1.

I have both the SMS-1 and the Denon 4806. The 4806's MultEQ auto-calibration system will work best wehen the speakers/system is set up correctly. The SMS-1 has insured that my subs are postioned, phased and overall integrated as best as possible. Plus, the 4806's digital signal path is only used in movies in my system. Hirez surround music is done via external inputs (ie not MultEQ'd) and my stereo signal path goes directly to my tubed preamp. In both cases, the SMS-1 has brought huge value.