I have not. There are some threads about the Esoteric XD series on the AudioShark Forums:
Here is a quote from a dealer posting there (Mike from Suncoast Audio):
The historically speaking there wasn’t always a major difference between the K1 and K3. But with the XD series, there is a significant difference between the K-01XD and K-03XD. I believe the K-01XD carries triple the number of delta-sigma chips over the K-03XD. Sonically, there is greater layering and a smoother presentation with the K-01XD. That being said, the K-03XD is a super performer at $14k and it’s the product that got me hooked.