You don't say which AES you are using on the H8000FW, but I'm going to guess that it is one of the back panel XLRs. This is because there is a difference here from our other rack units, as these cannot be used as sync sources. (see User Manual p.10).
I would suggest that you either use one of AES11-17, or WordClock as the sync source for the H8000FW.
