It is hard to know what the problem is without being there – it could be any combinations of bad cables, wrong settings or possible hardware problems. A few things to note:
1) The EXT light on the H8000 flashes whenever any routed input is unlocked, whether or not you are using it.
2) Since you seem to be relying on Wordclock, make sure that it is enabled and shows locked as described in the manual. Also make sure that it is connected and terminated as described in the manual.
3) If for unknown reasons you have trouble using the WC as a sync source, try using AES instead.
