HDMI passthrough audio does not seem to work

[Carol Abbott]

I have a Pi 4. I am trying to play a 5.1 ac3 audio file with media player using audio passthrough over the HDMI, using the command line:
mplayer /home/pi/pp_home/media/pluckTest.ac3 -ac hwac3

Without the -ac hwac3 command switch, the file will play, but only over two channels. I have the HDMI pi output running to an audio decoder, and from there to the surround sound system. I can play the ac3 file to all 6 channels using Kodi installed on the Pi, with channels set to 5.1 and HDMI passthrough selected in Kodi settings, so it doesn't seem to be a hardware problem. I have also tried adding "hdmi_force_edid_audio=1" to the config.txt file. No change_

the following messages are sent to the command window after the command line above is executed:

MPlayer 1.3.0 (Debian), built with gcc-8 (C) 2000-2016 MPlayer Team
do_connect: could not connect to socket
connect: No such file or directory
Failed to open LIRC support. You will not be able to use your remote control.

Without the -ac hwac3 command switch, the file will play, but only over two channels.
Playing /home/pi/pp_home/media/pluckTest.ac3.
libavformat version 58.20.100 (external)
libavformat file format detected.
[ac3 @ 0xb6815308]Estimating duration from bitrate, this may be inaccurate
[lavf] stream 0: audio (ac3), -aid 0
Load subtitles in /home/pi/pp_home/media/
==========================================================================
Forced audio codec: hwac3
Opening audio decoder: [hwac3] AC3/DTS pass-through S/PDIF
hwac3: switched to AC3, 448000 bps, 44100 Hz

AUDIO: 44100 Hz, 2 ch, ac3be, 448.0 kbit/31.75% (ratio: 56000->176400)
Selected audio codec: [hwac3] afm: hwac3 (AC3 through S/PDIF)
==========================================================================
AO: [pulse] 44100Hz 2ch s16le (2 bytes per sample)
[format] Sample format big-endian AC3 not yet supported
[libaf] Reinitialization did not work, audio filter 'format' returned error code -2
[libaf] Unable to setup filter system can not meet sound-card demands, please send a bug report.
Couldn't find matching filter/ao format!
Audio: no sound
Video: no video

Exiting... (End of file)

system info
pi@raspberrypi:~ $ uname -a
Linux raspberrypi 5.10.103-v7l+ #1529 SMP Tue Mar 8 12:24:00 GMT 2022 armv7l GNU/Linux
pi@raspberrypi:~ $ ls -l/lib/libc.so.6
ls: invalid option -- '/'
Try 'ls --help' for more information.
pi@raspberrypi:~ $ ls -l /lib/libc.so.6
ls: cannot access '/lib/libc.so.6': No such file or directory
pi@raspberrypi:~ $ dpkg -s libc6|grep ^Version
Version: 2.28-10+rpt2+rpi1+deb10u1
pi@raspberrypi:~ $