I tried the clocking ideas you suggested - didn't have total success using word clock in (possibly because there's an adat XT in the equation too which I didn't mention before!) - it's OK with the 168 and the 2408, but the adat can't locate a clock source. It seems ok using the optical clock option though I haven't tested it thoroughly yet.
One quick question - do the word clock cables connect directly to the 2408 and 168RC or , like PC's - do they need T-Pieces and terrminators as I haven't tried this yet???