speaker-test channel descriptions don't match expectations

[pfps]

The text output of speaker-test for -c6 appears to indicate that it is using 5+1 channels, with FL, FR, RL, RR, FC, LFE channels (output in a different order). But the wav files that it uses say FL, FR, RL, ??, FC, Rear Center. And this channel order doesn't seem correct, as the channels are not down-mixed to stereo correctly on my system with pipewire and pipewire-media-session.

What can be done to get speaker-test and pipewire to agree on the channels?