I also noticed this today. I recently got a computer with an optical cable out on it ( a desktop computer I always used laptops before) so I tried to connect and see if I could hear the computer's default Realtek digital output thru the interfaces headphones (useful for OBS monitoring before sending it out to network, if it would work) not a sound out of the headphones. Stumped. I have the 1824 and running the Universal Control I see the Spdif channel after the ins and before the adats in the mixer, but there is no movement in the mixer channel. I had previously not been using the headphones since I'm monitoring everything thru the 1810 further on in my chain. I thought I'd get the outs from a headphones here since monitoring thru the ASUS on the network via Network NDI is a pain because of Asus tendancy to prompt when headphones get attached, and play thru speakers if I just leave them in. So you can imagine that that would feedback in a mic and be a huge nuisance of unplugging the phones and replugging them every time I turn on the machine. Would be useful to get this 1824 working to play that monitor mix out of OBS. Any suggestions bump.
