I'm using pulseaudio on my debian system. My PC is connected to a 5.1 system. I enabled remixing, lfe remixing, channels, etc. in the pulseaudio configuration (speaker-test works perfectly). When I play stereo sources (vlc, youtube, etc.) no sound comes from Center and lfe. Looking at the volume meter (pavumeter) shows that only front/rear left/right get volume, center / lfe don't move at all. When I disable remixing, only front gets volume, so remixing itself is working (somewhat).
I'm using the software master volume to control the overall volume, i.e. the 5.1 system is a maximum volume and system volume is at 5-10%. When I turn up the system to 100% (and turning down the hardware volume), more and more sound gets "distributed" to the center/lfe channels (without actually getting any bass from the subwoofer). I tried tinkering with the channel map to no avail. Also, when I open the device in alsamixer and just push the master volume up and down once, all channels are at full volume, but then (in pavucontrol) the center and sub channel is always put at 100% volume and I can't further increase the system volume because one of the channels is already at 100%.
When bypassing pulse and using a simple lowpass filter / split setup in ALSA, everything works perfectly.
It seems that pulse uses the master volume of center and sub as relative volume, whereas the front/rear volumes are used as absolute.
aplay -l | grep card:
card 0: XFi [Creative X-Fi], device 0: ctxfi [Front/WaveIn] card 0: XFi [Creative X-Fi], device 1: ctxfi [Surround] card 0: XFi [Creative X-Fi], device 2: ctxfi [Center/LFE] card 0: XFi [Creative X-Fi], device 3: ctxfi [Side] card 0: XFi [Creative X-Fi], device 4: ctxfi [IEC958 Non-audio] card 1: PCH [HDA Intel PCH], device 0: ALC892 Analog [ALC892 Analog] card 2: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0] card 2: NVidia [HDA NVidia], device 7: HDMI 1 [HDMI 1]
Linux --- 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt25-2 (2016-04-08) x86_64 GNU/Linux
cat /etc/pulse/daemon.conf | grep -v ";":
enable-remixing = yes enable-lfe-remixing = yes # Same effect with = yes flat-volumes = no default-sample-channels = 6 default-channel-map = front-left,front-right,rear-left,rear-right,front-center,lfe