I own the K1xe, C5xe and just sold the Sony XA777es after enjoying it for 2 years. I have no knowledge of the quality of the third party mods for the Sony CD players, but I can tell you I have never heard a stereo better then mine with the addition of the C5xe. Its got base and trebble that didn't exist with the Sony. The layers of pure musical delight make listening as close to live as I've ever heard. My amp is a Krell FPB300cx which can probably be bettered by several brands and Revel Ultra Studios.
By the way I auditioned the C7x and it was only slightly better then the stock Sony 777.
By the way I auditioned the C7x and it was only slightly better then the stock Sony 777.