Digital Sub Out was not something I required. It was just my impression that this was the only supported configuration if I wanted mains to go digitally to external DAC. Turned out, I was wrong which is actually a good thing. It means one less external DAC for my planned system. I am perfectly happy with the Sub Out signal converted to analog by WiiM, I just prefer my main stereo channels to be routed to external DAC instead, which happens to have balanced outputs. My power amp does not have RCA jacks and also, I like my current DAC and have no reason to replace it with the WiiM Ultra one.