So I have exactly this drive too and had no problems with downgrading the firmware. I bought it about a year ago and was able to downgrade it without any problems, but still with the 11 version from DVDfab.
DonPromillo
Doing a little research, I discovered a similar model MD-8107
S-U3 (rather than MD-8107-U3) that is actually the drive referenced by DVDFAB as having official UHD support. Essentially, I didn't notice the missing "S" in the drive I purchased so I apparently bought the wrong one. Hopefully, DVDFAB is working on a solution to downgrade my drive.
Don, do you have the MD-8107-U3 or the MD-8107S-U3?