SPDIF, youtube aanother DAW

[Vhoot]

Folks
I've 11 Rack spdif hooked to a 2nd interface on another computer. The 2nd interface is connected to the main speaker. When I play my guitar through the 11 Rack, I can hear the sound through the speaker, which is way better than using xlr output. But there is no sound when I watch youtube or when I'm using some other DAW (Propellerhead Reason). In another word, I cannot route the main output from 11 rack into the spdif out. Is there any way to do this?
11 Rack (spdif) ---->Focusrite Saffire (spdif IN)
I've selected all the possibility of clock source (Internal, spdif) and matched sample rate between the two interface, does not seem to work.
Any help will be appreciated. Thanks