XRCD is a mastering chain, as gloco mentioned. Everything is strictly controlled from beginning to end, with much attention to detail, which should provide sonic benefits. They go to great lengths to avoid jitter in the chain.
I have about 10 XRCDs, and to be honest I don't like them. They are very bright, IMO, and the mastering isn't done all that well. Dunno, lots of folks LOVE them... But I just don't like the sound.
As for SACD vs DVD-A, I haven't heard the best of either to decide. I liked DVD-A better on the McCormack UDP-1 I had in house... But that certainly wasn't a fair test of format vs. format.
This guy has been dinging SACD since it came out, he has an interesting series of article starting here:
http://www.iar-80.com/page17.htmlInterestingly enough, the manufacturer of a high-end CDP had an in-house test of ~15 of the most expensive SACD players. He compared it with his most expensive CDP. The SACD players used SACDs, his CDP player used the CDP versions of each SACD. Only one SACD player was preferred over the CDP. To me, this says a few things: 1) SACD is far from mature and 2) 16/44.1 is maturing, and can be much better than we thought. However, what it told him is he needed to build a SACD player...