Surround Sound - not working in pulseaudio linux

**Background**
I use Arch based distro btw, EndeavourOS
Standard install mint desktop, with pulse audio
Sound configuration 4.0 (front left, front right, back left, back right)
It plays sound in general when playing some flac multi track surround sound.
It plays 5.1 flac downmixed to 4.0
BAR sees the sound system in the ingame audio advanced menu
PulseAudio sees BAR as SDL device with 4 channels configurable volume per channel (in pavucontrol).

**What is wrong**
When playing BAR it plays sound on front speakers only. Back ones not being used by BAR (but working in all other apps)

It also hears as back channels are being played along front ones, with one byte difference or overlapping so sound "flattens out" when maxing out int value on wave and speakers *bark*. Like 2 times the int value being sent to sound card.

**Summary as seen by GPT**
Something plugged wrong by SDL into pulseaudio - gpt says SDL mixer might not be ready for surround and has bugs with it,
OR
BAR not talking right to lib SDL


Start by reproducing the issue with the reported 4.0 PulseAudio setup and inspect the BAR advanced audio menu, SDL device channel mapping, and PulseAudio output in pavucontrol. Done means BAR uses the front and rear speakers correctly without duplicated or clipped channel output.

Written by the indexing model from the issue text.