I would avoid using the Toslink out on the Mac Mini. USB would be a better choice. You can get a DAC with USB support directly, or get a USB to spdif converter. That way you are not limited only to DACs with USB.
Zd542
Not in my experience. After testing each, I much preferred the toslink out. I feed it to a Monarchy Audio Super DIP which converts it to coax output which in turn feeds the PS Audio dac.