You can send the
digital audio over cat 5 as well. That was a quick google but not found a uk supplier yet.
For splitting theres
this. I wouldn't reccomend the cheaper unpowered splitters as they may cause problems with you sending it so far.Alternatively if you have digital coax output on the skyhd (only thomsosn don't), that will give you an extra output, so that could go to the local TV and the optical split using what I linked to.
Three amps with 5.1 setups in different rooms then. I always fancied going 5.1 in the bedroom but I doubt the missus would be happy.