X11 was improved X1, utilized the same architecture . apparently the mosfet problem was fixed in the X11 /111/1111
x11 came 3 years later.
Sonically, the AU 919 was supposed to be very close to AU-X1. AU-X11 was unique in that it has MM and MC, though MC impedance loading is limited to 40 ohms. IIRC, most other AU series amps had two MM phono inputs.