You are right – all H8000's ( and H8000A's ) have an ADAT board. On the H8000FW, this board is replaced by a FireWire board, which also supports ADAT.
This card can be removed by an end-user, but this configuration will not have been tested by us, so it may or may not do what you expect.
There is little reason for an H8000 owner to run 5.3, as almost all of its changes involve FireWire issues.
