Alexis,
I also noticed that my H8000FW
ADAT optical cables were loose in the
sockets.  
Tried both HOSA ?Premium?
and Acoustic Research cables?..no
problems with signal quality, but had
to secure the cables with plastic clips
near the H8000FW. (I am connecting the
H8000FW to MOTU 828MK3 via ADAT).

Final solution:  Monster  ?THX? brand
cables. Nice snug fit in the H8000FW, but
had to file down the plastic shell on one
cable due to the shell thickness  and close proximity
of the ADAT connectors.

JR