I haven't had a problem receiving DD 5.1 over the TosLink optical connected directly to my receiver. It's a pain to switch the Audio options in the settings menu to Dolby Digital, but I've gotten used to it.
The problem I'm having, though, is I've decided to connect just the HDMI to my Hitachi 50VG825, and then run the optical from the TV to my receiver. For some reason, the sound is coming through as PCM, rather than DD 5.1.
The tech at Hitachi says that the TV will output DD through the optical output, but it's possible that the SA does not support DD out through the HDMI. The owner's manual for the SA states that the HDMI does output DD.
So I can't figure out if the problem is with the STB or the TV...