The XK differs from the XP and X on one of the larger chips (lower right). Different brand, but I can't tell if it's the same type. The XP has a different kind of memory module than the X and XK. All three have different Firmware versions and slight differences in chips, jumpers, and overall PCB layout.
Radius Precision Color Pro 24X [v1.5 Firmware]:

Radius Precision Color Pro 24XK [v2.0 Firmware]:

Radius Precision Color Pro 24XP [v1.51 Firmware:

Radius Precision Color Pro 24X [v1.5 Firmware]:

Radius Precision Color Pro 24XK [v2.0 Firmware]:

Radius Precision Color Pro 24XP [v1.51 Firmware:
