/etc/default/pulse/daemon.conf shows channel map configuration as expected
but Pulseaudio is actually using
front-left,front-left-of-center,front-center,front-right,front-right-of-center,rear-center
the list of modules is very strange
first expected module is absent - module-device-restore
missing module should be in /etc/pulse/default.pa
in a block of 3 with the next 2 modules to restore streams and cards
but this device is what is messing up the channel map:
module-alsa-card device_id="0" name="usb-Corsair_Raptor_HS40-00" card_name="alsa_card.usb-Corsair_Raptor_HS40-00" namereg_fail=false tsched=yes fixed_latency_range=no ignore_dB=no deferred_volume=yes use_ucm=yes avoid_resampling=no card_properties="module-udev-detect.discovered=1"
did not realise this is a 7.1 surround headset until i checked the website earlier today
the unexpected names in the channel map make better sense in relation to headset
was not obvious when channel map was only 6 channels and not 8
but pavucontrol would show channels if headset level controls had been unlocked
my best guess is:
-
headset has id "0" detected by udev module and was likely plugged in before boot
-
alsactl does not throw an error and is ok with whatever channel map because there is no module to do database check, or is correctly using onboard audio channels/settings
-
when launched, pavucontrol can access the database and invalidate the channel-map to cause the alsactl errors, or headset takes default device status from onboard
setting to enable-lfe-remixing is ok
but will not have any effect because setting for lfe-crossover-freq
is still on default 0 Hz
i can find no information about this headset relating to Linux
i have no experience of this sort of device to suggest anything more about it 
suggest clear all previous changes in etc/pulse/default.pa and etc/pulse/daemon.conf and revert to default configuration
as both configuration files have been modified, there might be .pacnew files after Pulseaudio update (update will create .pacnew file rather than overwrite user modified file):
- delete the files etc/pulse/default.pa + etc/pulse/daemon.conf
- rename the updated files to remove '.pacnew' suffix
- reboot
if there are no .pacnew files; and not logged or cannot recall changes made, reinstall Pulseaudio
need to clear .tdb databases in ~/.config/pulse/ again (see post:9 item:1 above)
to remove any information about 6 channel headset configuration
suggest do not plug in USB headset until troubleshooting onboard audio completed
suggest install alsa-tools
and use hdajacksensetest
to check if 3 audio jacks are detected correctly if removed or plugged in
most of this discussion is now out of date and not relevant
original question is probably resolved by locking the audio channels in pavucontrol
suggest you do more testing and, if needed, start a new topic with full description and data for any remaining problems