HG,
I've bought all the XYZs in the past, and then all the ESP-ISK official releases released so far, and compared them.
The improvements aren't huge, but the ESP-DISKs sound better to me. More open sounding, and with a bit more detail. Only something for an Ayler nut who doesn't have original vinyl and never did to get really excited about I suppose. The Slug's material is possibly the most pronouncedly improved to my ears on my system. If starting out from scratch, I advise anyone to order the ESP-DISK cds from http://www.espdisk.com/