Originally Posted by sngbird
I don't know how and why but yes, for example, eq makes a big difference in my sounds through optical connection and this option are still disabled, see in the video.
OK, well it's doing that because you're also using Dolby Digital Live, that takes the "Speakers" output and encodes it to a DD signal and sends it out over optical. Remember, Dolby and DTS encoding is a lossy compression.
When you're not using Dolby or DTS encoding, you need that "play stereo mix over optical" option enabled. Yes, it's only stereo, but all the SBX effects works, so it great for headphone surround with an external amp - lossless PCM stereo signal.