FWIW, I had the EP500 and the UFW-12 in my house, and I ended up keeping the EP500. However, I can't say one was better than the other. They were different. I chose the EP500 based upon personal preference.

As far as THD measurements, I have seen THD measurements of the EP600. However, there has been some debate on how accurate those THD measurements are, and what threshold THD our ears can hear at low frequencies.