Last year, I picked up a Yamaha RX-675 because it was a well priced open box deal at Best Buy. Several people pointed out that Audyssey was a must have but I figured YPAO was close enough for my non-refined ear. Well, since then I've descended deeper into the rabbit hole they call home theatre and started realizing more and more what Audyssey offered. I've been watching the good deals forums, and have been seen the Denon X4000 dropping in price as the x4100 comes in. This week, it dropped to $799 on Amazon so I stopped by Best Buy yesterday and did a price match. I set it up last night, did the Setup and sat back and listened. I get that all this is as subjective as it gets, but my immediate impression was the sound was cleaner/clearer. Bass notes are much more pronounced and evident. My wife came down, and her first impression was that the sound was richer and more full. I watched a movie, and there was a noticeable difference in the sound and the surround atmosphere. Take that evaluation for what it's worth. I don't have REW graphs to prove it out, and I know it's subjective and the Internet is full of people trying to justify their new toy purchases. I was ready to take it back if it didn't make a noticeable difference in the sound, but so far the difference seems to be there. I don't think I'm going to be able to take this back. Maybe I could achieve the same with YPAO and REW, but I'm liking the automated option.