Which output device?

Hi, what do I select here if I have a regular non-i2s DAC (the DAC does have an I2S out but it’s currently connected via spdif/coax)?

Are you using a DAC HAT on the RPI? Then you can probably select it when enableing I2S DAC.

Yes. So I select I2S even if I’m not using the I2S out?

the HAT makes use of the I2S bus of the Raspberry Pi, converting the signal to SPDIF

so you should enable I2S DAC and select the HAT model connected to the Raspberry Pi

You can see the I2S here as the ‘language’ the RPI and the DAC use to talk. It is just a technical term you can ignore. Just indeed select enable and you can probably find your DAC used.