The PS Audio Ultra DAC will not be released until some time next year (probably in the first 4 months they tell me). Their new Digital Lens will come later. The iROC is being discontinued in favor of Larry's new MusicStream DAC, which is about double the price. You may be able to locate a used iROC. Be aware that it is USB only, so you will have to use USB out of your Mac Mini, not Toslink. I have an iROC on the way and can comment in a week or so (I also use a Mac Mini).
Both the PS Audio and Larry's new MusicStream will use the CEntrance USB software, and Larry's will also use some of the Empirical Audio technology. These, along with the Wavelength DACs and a few others, should raise the bar considerably for USB DACs. You'll probably be limited to 24/96 with them, although, technically, USB can accommodate a higher sampling rate.
Both the PS Audio and Larry's new MusicStream will use the CEntrance USB software, and Larry's will also use some of the Empirical Audio technology. These, along with the Wavelength DACs and a few others, should raise the bar considerably for USB DACs. You'll probably be limited to 24/96 with them, although, technically, USB can accommodate a higher sampling rate.