Problem with Mac mini

Hi all,
I just purchased mac mini to dedicate it to my music and thus free up
my Imac for home use.I am having problem getting it to work.
When I connect it to my DAC using Bel Canto usb to coax converter it
will not sync with my DAC so there is no sound coming out of speakers
even though I chose Bel Canto in sound preferance out.
I thought that there was something wrong with my DAC or Bel Canto,
but When I connect my Imac the same way it works fine. I took it back
to Best Buy to Geek Squad, and they could not figure it out.

I hope there is somebody out there who can help me with this problem before I take it back for good.
I thank you all in advance for your help.
Regards,
Rod