Not sure why no one has replied as yet...
Since I'm on this thread, just about waiting for things to warm up... I have heard both these units. If you're referring to the K07XS & the K03XS, I've heard the latest 'XS' units and currently own the K07XS.
The top of the line have been modded to the XD series now, so the XS is offered in the 07 and 05 series. Pretty much the same, with very subtle differences for a fairly big margin in price difference. Then comes the K03XS series and above and things get serious. The DACs are upgraded with a different bit layout topology, plus transport mechanism is top of the line. The significant upgrade is the clock. However, even with the K07XS you can install this very same upgraded external clock, which takes the performance further towards their top tier stuff. So it gets very interesting having to choose from either an all in one unit or two separate chassis which are dedicated functions.
Then if you want to go really crazy, Esoteric also offers a mothership of digital gear, where the DACs, Transport, and clock are all separate to the point where the DACs are monoblocks, one Dac for each channel! Haven't heard this config as yet but was going to this Feb. Obviously Int'l travel is restricted, so we're going no where until next year I guess.
The K03XS series is improved and the XD series is improved even further, so I guess at the end it depends on your personal preference and particular setup you have.
Sorry it took nearly a year to reply!
Hope you get this message though.
Cheers and all the best, RJ
Enjoy those fine tunes!