There is no need to have it synced perfectly.
As I watch movies, I use the sound which comes through the HDMI, which will be multi-channel.
But if I want to listen to music, I’d like to use the better 2 channel USB DAC. I don’t want to turn on any screen to change any configuration.
I don’t mind if it’s a (couple of) frame behind, since it’s gonna be used for music only, or you can change the delay in the receiver.
If it’s a matter of changing some config file, that’s fine too. I found a thread on this here, but I don’t know if it’s useful.
https://discourse.osmc.tv/t/usb-and-hdmi-audio-at-the-same-time/10966/9
Thanks!