Oh sorry, I thought you weren’t able to load the different channels. Surround sound is an exotic solution for Squeezebox. Here’s what I wrote on the subject last year:
So far, there has not been a lot of requests for 5.1 audio playback in our community. Most audiophiles prefer 2.0, or in some cases 2.1, for which we created the Piano 2.1 DAC solution.
But generally, Squeezebox was designed for 2.0 playback and your best bet for anything with surround sound is using Kodi 😉
Some people use 7.1 cards to play to different channels with different players. But surround sound for music is not a usual application.