Tip: Unplug USB Headphones for audio passthrough on Shield

After recently doing a total reconfigure of my HT setup to incorporate the PS5 and Series X, I've been plagued with a lack of AC3 passthrough from my 2019 Shield into my Denon AVR. The Shield would only ever decode AC3 from ATSC channels into PCM in 2.0 / 5.1 (dependent on content source) in apps such as Plex, the official HDHomeRun app, and Channels (only in 2.0, and only after disabling Surround Sound support). If I enabled the Surround Sound option in Channels, then there would be no audio at all. I could use the native ATSC tuner in Kodi and force AC3 passthrough, but that was pretty much the only way to get passthrough to work on standard AC3 audio sources.

Finally, after much consternation, I determined the cause of my headaches for these past few weeks. In my setup, I have incorporated a USB Switch Hub so that I can share my wireless headphones between the my devices (Shield/PS5/XSeX/Switch/Mac/PC). While the Shield has an option to force the audio output to a specific device, such as being able to select either HDMI or the wireless USB Headphones, simply having the USB Headphones connected as an available device, even if outputting audio over HDMI, apparently completely disables AC3 passthrough!

This was quite confusing since higher bitstream formats such as DD+ and TrueHD are still passed-through to the AVR without issue. In trying to research the cause of this issue, I've seen various other reports of audio passthrough problems with Channels and the Shield. This isn't to say that my setup is the same as those other reports, but my advice would be to make certain nothing else in your setup is similarly affecting performance like it was in mine. Thankfully, the USB Switch I purchased has infrared remote capabilities, so it is easy enough to script things with my Harmony remote so that under general activity startup, the USB Switch isn't enabled for the Shield and I can connect the headphones ad hoc when desired without having to get up from my couch.