It's as mikeyko alread said: over spdif you can only pass unencoded stereo and ac3/dts.I am currently using SPDIF to pass audio to my receiver. I have a video card that can pass LPCM audio through HDMI but my current receiver does not support it. I have ASIO4all and use it with this plugin. I can play multi-channel DTS files and DTS and AC3 Audio from movies without issue. There are two places where I run into issues: Multi-Channel FLAC files and DTS Audio ripped from DVD's. The latter will not even play.
In order to play ac3/dts over spdif with this plugin, it needs to be encapsulated in 2 channel PCM. Audio ripped from a DVD is in raw format and thus will not play. You can encapsulate it though using the spdifer tool from AC3Filter tools | AC3Filter