Bottom line, I guess: PulseAudio in 2017 _just effin' works_.
Just effin' works? You gotta' be effin' kiddin' me.
Pulse is _barely acceptable_ if you ONLY deal with stereo.
If you're using 5.1, or better yet, 7.1, you are sooooo fucked.
1. Pulseaudio has "enable_remixing" enabled by default.
This effectively ruins stereo content when played back on surround hardware. It sends L to L, SL, BL, and C. It sends R to R, SR, BR, and C. Do you see the problem here? C=L+R.
Bonus, it will also synthesize a LFE channel for you. LFE=L+R lowpassed at 200hz.
This can be disabled in the config file. I've never seen any pulseaudio manager with an option for it.
2. ZERO of the about 40 linux games which support surround in my steam library actually work properly in 7.1. (This might be steam runtime's fault). It invents channels that don't exist in a 7.1 configuration. Instead of SL and SR, there is a Front-Left-of-Center and, Front-Right-of-Center.
If remixing is disabled, you will have no output on SL and SR. If remixing is enabled, you will have incorrect output on SL and SR (A mix of the front and rear channels).
3. If you're trying to set up 5.1 over optical SPDIF, may god have mercy on your soul. Good luck getting it to output 5.1 DTS. I was only ever able to get stereo, but I hear it's doable.