WDTV Live still an optical signal when switched off

Ive just added a Harmony remote to my setup and got everything up and running perfectly, my only problem is my 5.1 amp is an old one so only has one optical input which my wdtv shares with my Sky HD box, so I run the optical cables into a spliter which then goes into the amp, meaining if they are both sending a signal then I get no sound at all.

As part of the activities I have I have watch WDTV in 5.1, watch Sky in 5.1, but when I switch of the WDTV it still sends a signal down the cable, the only way to stop it is to switch the power off at the mains, but that means my Harmony remote wont run the activity correctly as the box is off at the mains

So is there a way to power down the WDTV box into a standby mode where the optical signal goes off as well?