restock - the output on the mac can be for analog or digital. if you buy the cheap mini-to-rca cable from monster, you will get analog. if you get a quality toslink cable and buy the mini adapter for it, you will then have a digital cable. what happens is this mini-toslink adapter is a little longer and allows the digital signal to come thru. i use this method in my setups. the mini to rca sounds terrible.
its interesting that you think benchmark dac w/usb was far better using the usb connection. all the reviews indicated that the usb connection was inferior to the coax and toslink connections. i also listened to the benchmark and the bel canto dacs with usb connections and they were inferior to the coax and toslink connections. i preferred the bel canto over the benchmark. but i also preferred other dacs over the benchmark but they cost much more. also, these more expensive dacs only use glass,coax,toslink, and bnc, no usb with good reason.
if you want a quality dac using usb, check out the new audio research or ps audio dacs. i heard the ar at rmaf and it sounded very nice. did not do any comparisons with the other connections but the rep told me that they designed the dac to make the usb connection every bit as good as the other connections, something that the prior vendors didn't do. i also talked to ps audio at rmaf and they were working on their latest usb dac.