Hello Everyone,
I no longer have an ONYX, but I now have a hacked DPT-RP1 so I was forced to find an alternative to the HDMI monitor input. I had previously used VNCViewer but the delay was too severe. Then I discovered 'Spacedesk'
Spacedesk essentially turns any android tablet into a wireless monitor WITH touch. (similar to iDisplay and Splashtop I believe) Mirror or extended desktop are both options. MUCH faster than the VNC method, and possibly as fast, if not faster, than the HDMI input on the Boox Max 2.
Spacedesk is also free and runs flawlessly on my Dpt-RP1, I'm sure it would also run smoothly on most Boox models. Enjoy!