Im assuming you set the MR to External Clock via ADAT in the Setup on the MR Console?
I would try the Wordclock route and see if that will fix the issue. Im guessing the MR just is not cooperating in changing its sample rate for you via the ADAT connection. Standard Coax cable to use for Wordclock is cheap . BNC Connector.
MR is finicky IMO
IF no resolve I would look at selling off the MR and getting a diff 8 channel unit
Our FW boxes are becoming an issue Im afraid