HiFiBerry Digi+ I/O Overlay/Settings

I have broken out all my older RPi-3s which all have HiFiBerry Digi+ HATs on them, and they work great with the different amps and devices around the house (I used to use them with Rouge Amoeba’s AirFoil and the Pis with SharePlay). I have currently use Echo Links/Echo Link Amps for multi-room music, but I am trying to ween myself off of the Alexa ecosystem. I have everything working great with balenaSound, but I really miss the digital line-in distribution feature of the Alexa devices.

I recently received a HiFiBerry Digi+ I/O to see if I can get digital audio into the Pi to send around the house from internet radio stations via VLC (sound source is macOS, output via USB S/PDIF device, which I have fine control of the bit-rates, and is known working for output to the Echo devices) but so far, no go with the Digi+ I/O. balenaOS sees the card but I can’t seem to get it to light up the inputs with I probe it with alsamixer via the terminal.

Is there a specific overlay I need to use other than hifiberry-digi ? I have a HiFiBerry DAC+ DSP on order, which may work better (and seems to have a listed overlay in the documentation), but my curiosity is getting the better of me trying to get this to send to the multi-room setup. Are there any other arguments for SOUND_ENABLE_SOUNDCARD_INPUT when I add that customization?

Any advice is appreciated - thanks!