Control point for USB port ?

[Cebolla]

Isn't the OP effectively asking for a UPnP renderer that can be installed on a Mac Mini, so playback and output via USB audio to the mentioned DCS Elgar DAC?

The only reliable UPnP renderer for the Mac I know of comes with the JRiver Media Center. It also comes with a built-in UPnP media server and UPnP control point for external UPnP renderers, but its core functions are that of a standard music player with its own media library for the computer itself (like the mentioned Audirvana) - the UPnP components are just ancillary functions. It is an all or nothing approach, as there is no way of unbolting its UPnP components from its main function of a music player and library.