There is an experimental feature in balenaSound that allows using a sound card input rather than one of the wireless protocols. See  and  below. You will need to add a supported sound input device, such as a USB sound card or a Pi Hat that provides an ADC or digital input. See  below. This is still experimental, and you may have to tweak things.
You may lose the Dolby portions of the audio. Only some parts of balenaSound support audio with more than two channels. Although it should pass through without being lost, you would have to decode it for more than stereo sound, which would require external equipment, if it’s at all possible.
Also, note there is an audio delay (approx 2 seconds) that will make using balenaSound with video a challenge. The delays are part of the system’s design, so that the audio can be kept in sync across many devices over a network, without gaps and skips in the audio. You can adjust the latency to some degree.  But you cannot totally get rid of it. If your video source has some adjustments that allow you to sync video to audio, you may be able to correct for it in your system.