Volumio SupTronic X400 - using the RCA connectors

Not really a volumio question per-se, but I have a Rasp PI with volumio running through a suptronics x400.

I note the x400 also has rca connectors for input, and did see a recommendation to mute the DAC on the x400 and it will output the RCA connector feed. Would there be omething that the Volumio UI could trigger to short out the mute pin on the x400. I’d need some sort of GPIO triggered switch over the mute header that can switch it between mute and unmute.