I can't help with any personal experience of those chips and their differences. There's a lot of info on the web though.
Yesterday I'd have to say the SCD-XA5400ES won out over the ZDAC by a few hairs. When I'd compare, toggling back and forth with the ZBox, the Sony just had more warmth and more refined sound, a very integrated and clear sound. In comparison the ZDAC had a huge sound that lacked the warmth and coherence of the Sony, to a degree. A fascinating whirlpool of sound though, that was cohering gradually through the day. I'm very impressed that the ZDAC has the same degree of clear and extended tonal balance that I found so distinctive in this Sony player. In this sense, in my opinion, the ZDAC has already surprassed my seasoned ZCD. The ZDAC was shut off over night and is doing very well as it warms up with one of my favorite 'test' discs, the most recent US cd release of John Coltrane's 'Crescent.'
I'm already convinced that the ZDAC is a great machine that will be getting better day by day for a spell. In my opinion the Sony is a powerhouse player that is hard to beat., I'm so glad I took a chance on it. I found an interesting review of a modded version here:
sonyscdxa5400es
Within the review it mentions:
"The 5400 model is a direct coupled voltage design and with no capacitors in the signal path. We all have been told that the sound of a capacitor should be to have no sound. That has been accomplished here by the process of elimination—there are none in the pathway."
That signal path seems to give it a distinctive sound that really works well with my tastes and system. The SACD output from this player was the first that really excited me, and the redbook output is still my personal referrence sound, the best I've ever had. (It's build quality and frame design have led to this being an excellent transport as well).
Already the ZDAC driven by three sources (immediately improving the sound of two) has shown itself to have a wonderful, detailed, dynamic sound. And it's design is very different than the Sony's analog output stage, with all those capacitors (if I understand correctly; I may be wrong). This illustrates Steve's discoveries that different pathways lead to sonic success. Adding the ZDAC to my system has been a win-win.