I have the same question.
The M68 OAG info says: "6. For guiding, only can work with ASI mini camera currently." It does not say why, so I thought it might be the backfocus difference, but that is a guess.
I know that with the 071 and at least some other "main" cameras that have the USB2 hub but support USB3 (and any other USB3 connection), that if you connect the 174 or 290 mini USB2 cameras, you can only use USB2 to run the main camera... I wound up purchasing the 120 USB3 to keep from having too run separate cabling, etc. just to drive the autoguider. From your specs, even this won't work now.
So, do you have a USB3 mini? Or will this actually work with the 120MM USB3 (non-mini)? Or is there a fix for the USB2 problem? Running a high pixel count camera is rough on USB2, and I have to modify my NUC to even support USB2 (and some laptops don't even have it anymore).
Thank you!!
-Mike