SUMMARY
***
Surround 5.1 channels are mixed/mapped-up incorrectly using pulseaudio
This can be fixed by a unusual tweak of the channel-mapping..... 
This is related to interfacing pulseaudio via surround 5.1 
***

This is a duplicate of: https://forum.kde.org/viewtopic.php?f=305&t=175181

STEPS TO REPRODUCE
1. to get 6 channel audio output it is necessary to modify file "/etc/pulse/daemon.conf" by adding 6 channel-map;
default-channel-map = front-left,front-right,rear-left,rear-right,front-center,lfe

2.) to beware of recall of last restored card or device info best un-comment
all "load-module  module-*restore*"
lines in pulseaudio file /etc/pulse/ default.pa

HINT: the channel-counts MUST NOT be set explicitly, 
;;;; default-channels = 6 
is default-channels are set, the resulting channel-map is completely weird

  
Possible PROBLEM:
    are the correct channels chosen when pressing KDE->SystemSetting-> Audio->Extended->Speaker-Test  ?

OBSERVED RESULT
Neither a check of speaker-channel mapping  shows  the correct channels usage of surround 5.1
    speaker-test -c6
nor
     KDE->Systemsettings->AUDIO->tab:Extensions->Control Speaker Set 

EXPECTED RESULT
both of the two tests shown above should work correct.

SOFTWARE/OS VERSIONS the used platform is a raspberry PI-400
Windows: 
macOS: 
Linux/KDE Plasma:  Linux kderaspi 5.15.32-v8+ #1538 SMP PREEMPT Thu Mar 31 19:40:39 BST 2022 aarch64 GNU/Linux
KDE Plasma Version: 5.20.5 
KDE-Framework-Version: 5.78.0
Qt Version:  5.15.2

ADDITIONAL INFORMATION; WORKAROUND
I found a workaround to get correct audio channels by tweaking the channel-mappings.

by tweaking the default settings:
    front-left,front-right,rear-left,rear-right,front-center,lfe
to
   front-left,front-right,lfe,front-center,rear-left,rear-right
in pulsasudio daemon config configuration and alsa-mixer/profile-sets


#### details of workaround.... the position and ordering of "...,lfe,front-center,..." is eminent.
#FIX-part1: modifying /etc/pulse/daemon.conf by adding 6 channel-map values AND using "lfe,front-center" in this sequence
; default-channels = 6 // channel-count MUST NOT be set, otherwise resulting channel-map is completely weird
default-channel-map = front-left,front-right,lfe,front-center,rear-left,rear-right

#FIX-part2: vi /usr/share/pulseaudio/alsa-mixer/profile-sets/default.conf
[Mapping hdmi-surround]
description = Digital Surround 5.1 (HDMI 0)
device-strings = hdmi:%f
paths-output = hdmi-output-0
channel-map = front-left,front-right,lfe,front-center,rear-left,rear-right
priority = 8
direction = output