Bug: Hardware that does not support s32le - sndiod -dd shows s16le

If I run

$ mplayer -ao alsa:device=hw=1 -af format=s32le _AUDIO_ONLY_FILE_

On my Chromebook Pixel 2015, mplayer responds with

[AO_ALSA] Format s32le is not supported by hardware, trying default.
AO: [alsa] 48000Hz 2ch s16le (2 bytes per sample)

Audio plays fine.

I try s32le in 2 different ways, in my $HOME/.asoundrc file,

=============================
Method 1 - set s32_le in type slave { }
=============================

$ cat $HOME/.asoundrc

pcm.sndio {
type asym
playback.pcm "sndio-play"

hint {
show on description "OpenBSD sndio"
}
}

pcm.sndio-play {
type plug
slave {
pcm "sndio-raw"
rate 48000
format s32_le
channels 2
}
}

pcm.sndio-raw {
type file
slave.pcm null

format raw
file "| aucat -f snd/0 -i -"
}

pcm.default sndio

=======================
Method 2 - set s32_le in aucat
=======================

Comment out rate, format and channels in slave { }