Just wanted to chip in here and say I have also installed the new 5.61b and it is working fine here now. I have also got it connected via wordclock and adat, but I also connected it via firewire. When I first installed it I had the same issue as you and the ADAT kept slipping so I opened up the new version of Dice after installing it and set that to wordclock and then on the H8000FW I held the program button for a couple of seconds until the routing selection shows up and set that to the ADAT In and Out preset and then saved that as the default routing preset when starting up the H8000FW. I also ran the routing utility program and did the same thing there and set that back to my previously saved routing preset which does basically the same thing as those routing presets on the H8000, but I just wanted to double check it worked ok too.
Finally I did a reboot and the ext clocking works fine and so far v5.61b is working very well here.
So first of all have you installed the Dice program and set that to wordclock or adat sync and secondly did you reset the routing preset back on the H8000.
I'll have a look again at my setup to see if there is anything else that might help you, but hope you manage to get it working anyway.