Turns out, the problem was with pipewire upmixing not being enabled by
default. After copying /usr/share/pipewire/pipewire-
pulse.conf.avail/20-upmix.conf to
~/.config/pipewire/{client.conf.d,pipewire.conf.d,pipewire-
pulse.conf.d}/20-upmix.conf (not sure which one kicked in) all the
channels in the 5.1 configuration started working.-- Best regards, Sergey Matsievskiy
