Raspberry Pi Audio - Can not get 5.1 Surround Sound Audio to output to HDMI

Question

I have an applications where I need to do the following on a Raspberry Pi (3, 4, and/or Zero) running the latest version of Raspberry Pi OS:

1. Play an AC3 file with 5.1 audio over HDMI.
2. Play an MP3 or WAV file to a specific speaker in the 5.1 audio over HDMI.

I am currently using OMXPLAYER and have tried some of the Pulse Audio and APlayer approaches I found in other places but no luck so far. The problem is that I can not get the output to the HDMI port to be 5.1 as it keeps downmixinpg it to 2 channel audio.

Does anyone know how to get this to work?