I've got both the 750 (2 months) & the 555ES (14 months). I bought the 750 for DVD-A & it sounds awesome. I actually haven't compared the SACD of the 2 players (my initial out of the test box of SACD didn't seem to be better then the 555, but then I didn't give it much of a chance). I plan to do an SACD comparison this weekend & I will reply on Monday.
The things I don't like about the Yamaha (which are minimal compared to how much I love the DVD-A sonically) are:
the remote
no dedicated fast forward button (you have to hold down the track button),
loading (someone else mentioned this, I get around it by using the exchange
feature rather then the open feature, you can't get all 5 out at the same
time, but you have easier access to the 4 you can. When you press the
open button 2 of the discs are awkward to get out).
DVD-A discs do not auto advance to the next disc when done (this kind of
defeats the purpose of it being a changer)
This unit was bought to replace a Mitsubishi DVD-A that had varying problems with 5 discs in my collection. It was purchased 2 days before Christmas when the store was out of all single disc players that I really wanted. Driving home I had plans to return this unit for a single disc player after a couple of weeks. After hooking it up I was blown away with the audio quality of DVD-A's I've been listening to for the last 3 years on the Mits. I went throught most of my collection the next day and was amazed at the difference. There are times I hear things I've never heard before. I realized a return was now unwarrented.
I used to be much more of an SACD fan. DVD-A sounded great, but I wasn't WOW'D like I was with most SACDs. While I still prefer SACD, with this player DVD-A it is not as discernible of difference as it used to be for me. I will let you know what this weekends test reveals. Of course all the above is IMHO and I hope both formats are around for decades to come.