No sound from Meridian 218 dac/reamp from Roon Mac App

I have a Meridian 218 feeding a Parasound amp into my Martin Logan speakers. Other inputs work fine. I believe I’ve configured the 218 correctly (using the Sooloos input and 4C comms channel). Roon detects it no problem and even directly controls its volume no problem (I can see moving the volume slider on my Mac Roon app updating the Meridian Control volume slider on my phone). It plays in the app but no sound comes out, even at top volume.