Rob,
I am not trying to sell anything, I am just throwing in my 2 cents on my XA777ES experience. The $550.00 is not for a DAC but for a TRL mod. Before I bought my 777, I read a lot of reviews, most were very good and a few were very bad.
I thought that the bad ones were just Sony haters or very anal. I was surprised when I got my player,andIhad others listen too. The SACD was far better than my SCD333ES. The Redbook was much more detailed than my 333,but it was a very flat,dark and analytical sound with very little sound stage, at least on my system. I called around and not many people will mod a 777 and those that will for $1500 don't really recommend it because the newer players have better chips. So I thought sell+get a DAC but that also means a few cables that take a $1000 DAC price up to $1500 or more.
So the most affordable upgrade was to give the TRL mod a try. I really like it, and I think it is a good deal at $550.00 Have fun !
Frano