"Could just be more people coming to terms with the fact that the sound quality difference between a $500 Dac and a $3500 Dac is very small relative to upgrades like better speakers or adding room treatments and they're just going to put a bunch of money back in their pockets. Or it could be something else."
In order for that to be true you have to assume there really is a small difference between a $500 dac and a $3500 one. It may be true in a few cases, but I don't see any evidence to support that claim overall.
As to why there are a lot of people selling the Ayre dac, I would say its perfectly normal. Ayre is one of the bigger high end companies. The more dacs they sell, the bigger the used market is.
The most likely reason that I can think of, is that the dac owner doesn't know how to set it up for best sound. Its not plug and play like a CD player. You have to rip disk's the right way, configure your PC, use and configure your music software, configure your home network in many cases. etc..
"I've heard several Dacs using the ESS9016 and they all sounded wonderful, so I'm sure the Ayre is a fantastic Dac as well."
It may sound fantastic, but there's more to it than just the chip. One thing I've noticed from reading many comments on this subject, is how almost no one brings up the analog section of the dac. It contributes at least as much, if not more to the sound, than the digital portion. The Ayre dac is the perfect example of this. Ayre has a very unique sound that I've never heard duplicated by any other brand.
