Re: Multichannel audio playback

[didier gaumet <didier.gaumet@gmail.com>]

Did you adjust the volume of output 3 and 4 in alsa? if you are lucky, 
the routing is correct and these outputs are only muted.

But I think (no pun intended) that in your present case, you need to 
learn about:
- mixing and mastering (partcularly routing)
- particular abilites or limitations of your Behringer interface
- linux low-level tools if that is what you want to use
That's why I suggested you to use GUI tools, because, while perhaps 
sometimes bloated or in certains cases not offering certains options 
that a CLI tool proposes sometimes, GUI tools are more intuitive. And 
it's easier to learn only mixing/mastering than mixing/mastering and 
linux audio internals at the same time.

As a starting point a tutorial about audio routing could be of use to 
activate outputs 3&4 and chose what to feed them in (sorry if this is 
not a correct sentence, I'm french). There is the routing chapter of 
Ardour tutorial:
http://brunoruviaro.github.io/ardour4-tutorial/understanding-routing/
but the whole tutorial could be of interest

Cheers