That would be my preference also, mainly because the Mac Mini only has an optical out. Unfortunately this would mean some sort of optical switch box as the Playstation 3 that U use for Blu-Ray also only has an optical. This wasn't an issue with the 7510 as it had 2 optical inputs.
I will be interested to dee if can see a difference between the optical out of the mini and the USB. In OS X midi setup I set the optical to output 2ch-24Bit at 44.1Khz. The 7520 is at 2ch-16.