5.1 audio from MBP USB-C to HDMI

I am struggling to get surround sound from my 2020 MacBook Pro (Intel version).

I also have a 2015 MBP that has an HDMI port which I connect to my Denon AVR and it gives me glorious Dolby/DTS 5.1 whilst passing the visuals to my TV. So I know my media is fine.

My 2020 MBP only has USB-C ports. So I first tried with this USB hub that has an HDMI port. My AVR only sees 2 channel audio and the Midi app in MacOS only shows 2 channels being available.

I have also tried this USB-C to HDMI cable and get exactly the same results.

The manufacturer of the 2nd cable couldn't get it working either and issued a full refund.

So how can I get HDMI surround sound from my 2020 MBP?

I've read it could be an issue with how the USB-C signal is being converted and maybe using DisplayPort as the middle man, but is this a quirk of the MBP or the adapters?

I believe your problem is that the HDMI adapters you tried so far only support stereo audio, to get 5.1 audio requires an HDMI adapter that supports it.

In these USB-C HDMI cables is a small system-on-chip computer that does the conversion from the native DisplayPort (or "DP") to HDMI. That computer in the cable will have to tell the Mac what kind of audio and video to output, then do the conversion, and if the chip in the cable was programmed only to handle stereo audio then it's not going to provide a data path for the six audio channels needed for 5.1 surround sound. DP supports 5.1 audio, HDMI supports 5.1 audio, but that doesn't mean every adapter from DP to HDMI supports 5.1 audio. Look in the specs of the adapter cable for the number of audio channels it supports, if it doesn't tell you then assume it supports only two channel stereo.

I was curious if I could find a DP to HDMI adapter that specified the number of audio channels it supports, and that the number supported was more than two channel stereo, and found this: https://www.startech.com/en-us/audio-video-products/cdp2hdmm5mh

I have no affiliation with StarTech other than being a customer in the past, most of all they just happened to be near the top of my search results when looking for examples.

If your display has DP input then maybe you should use that instead. By using the DP input there is no protocol conversion in the cable, the cable should be less expensive and not limit your audio options.