Combine 2 hardware devices into 1 sndio device

Hi,

Is it possible to combine or merge two hardware devices into a single sndio device?

My use case is a USB webcam with mic, and an external USB audio interface for my headphones. When making video calls in Firefox or Chromium I can use either the mic or headphones, but not both at the same time. Both web browsers use the 'default' audio device (snd/0) and don't list any other devices to choose from.

Since this is a FreeBSD system one thing I can do is attach sndiod to the mic and expose that as snd/0, then let audio out fallback to FreeBSD's default (which I can set as the USB audio interface). This means the audio out is not controlled by sndiod, and is hence quite loud.

Thanks,
Tim