Yes but, apparently, there is no guarantee that the Touch's USB mod will work with all DACs. For that reason, I would not put all my e$$s in the USB basket.
I would imagine John Swenson could give you some tips on what type of USB DAC would work best so you could inquire of each company if their USB DAC fit the correct parameters. Just a guess though.
On a different note, am I the only one who thinks Ayre missed the boat by having a USB only DAC? I would have thought the QB-9 would've sold many more units if it had a coax/toslink in as well. Of course, I'm no DAC designer so I'm speaking purely from my @$$ on the subject.
FYI, if the Touch USB hack doesn't work you can get a used Mac Mini for essentially the same price that you can sell the Touch for and turn it into a Squeezebox with software like Squeezeplay. Of course there's lots of other Mac software that people use, but I would never give up the excellent Squeezebox interface.