Hummm, thanks for making things clear enough.
Now, one question...
¿HOW are you trying to send "raw" AC3 /EAC3 streams into those AUDIO devices you tested?
Because SPDIF is meant to transfer 'pure' uncompressed audio OR lossy compressed audio through an LPCM audio "wrapper" (so to speak). An *actual* SPDIF stream can transport not only AC3 and DTS, but also MP2, MP3, and even WMA and AAC
Therefore it is expected that an audio card or something similar will reject any SPDIF signal that it does not recognize as 2-channel LPCM audio...