My first mistake was not accurately stating the problem. I have a Roon nucleus and two DACs, which I want to be able to select depending upon the streaming source I’m using. I forgot that the nucleus has two USB outs, and I can select the DAC that I want from the preamp. What I can’t do at this point is to find my stored high-resolution files on a USB drive attached to my Mac mini. When I go to the storage selections on Roon it allows me to add a network share but does not allow me to browse to find the USB hard drive attached to the mini. Does anyone know how to ‘see’ the network from the Roon software on my iPad? Sorry this was so convoluted.