Let us know what you find. When using Toslink out of the Mac Mini, open the application called "Audi Midi", choose the external output and set it to 24-bit and 96KHz.
I finally had a chance to mess around with this a little. I connected my Mac Mini to my TacT RCS 2.0 via optical (toslink) connection. I listened to just the Mini for 15-20 minutes before doing any comparing to other sources.
At first listen, the Mini actually sounded pretty good. Good detail and extension, smooth and decent soundstage. My thoughts were, "not bad, I could live with this".
Then I compared it to my SB3 with Bolder digital mods and a Bolder power supply. It wasn't even close. The SB3 had a larger, deeper soundstage, the lows were deeper and tighter and the highs were more extended, with more air/space around them. The SB3 sounded all around fuller, tighter and smoother. The Mini, in comparison was very thin sounding.
My next step will be to try the Mini via it's USB outs, but that won't be for a while, as I don't have a DAC with USB inputs.
I really enjoy the sound of the SB3, but I don't like the interface. The Mini, being controlled by an iPod Touch would be perfect. If I can get it to sound better.