nvidia – how to set pipewire audio over HDMI as default on Kubuntu 24.04LTS

I’m running a Kubuntu 24.04LTS (X server) install, mainly for use as an HTPC with mpv as the video player.

There’s a Nvidia 4060FE GPU which uses one of its HDMI outputs for connection to an AV receiver, which drives the speakers and the TV monitor. There’s a second control monitor attached to the GPU via HDMI, which also has built-in speakers. These speakers are terrible and only for emergency use.

I want a setup where I can set the used HDMI output on the graphics card as default, with all the settings (5.1 surround) as necessary.

What’s the best way to do this? I know that Kubuntu saves my last-used settings, but every so often, the PC gets confused and I have to reapply settings.