Sorry but this is not true. Optical is capped at 44.1khz when doing 5.1
It is capped at double that when doing 2 channel, possibly 96khz
Some recording interfaces use 2 optical cables to achieve a higher bitrate.
Hdmi 1.4 caps at 192khz with 7.2 channels, hdmi 2.0+ can do alot more channels at 192khz
You're right HDMI can be faster than TOSLINK. Your thin client wasn't made to do multimedia hocus-pocus, so I'm skeptical that you get higher bitrate on your DVI output, which wasn't designed to play audio at all.
Please open a new thread for "Castanigit" (?) at the add-on sub-forum.