Noob Question (select Audio Output)

Hi Community, I’ve had a search for the question, it may be too basic…I’ve just got a Mercury V2 streamer and using Volumio, I can’t select an Audio Output other than HDMI, that’s the only option offered. I’m using SPDIF, that’s plugged into a digital pre-amp, so it may be that no DAC is visible through that connection, hence no option offered? Everything else is OK, library is there, just actually getting output! Are all outputs live anyway? Thanks and apologies if this is trivial or wrong place.

it says here that you have to select HifiBerry digi+ pro.

Thank you, I did that initially but whilst familiarising myself with settings and updating Volumio to the current version, that option is no longer available, all that is showing is HDMI. OK just spotted I had i2S DAC set as off, switched to on and we now have music! Thanks, the photo showed my error. Good one.