I would not recommend using the Touch with a USB connection to a USB DAC unless you already own such a DAC. There is little advantage over using S/PDIF, especially considering the inconvenience.
Keep in mind that if you are planning to use USB you are not streaming anything. For streaming you would need the PS Audio + Bridge. Future proof USB DAC is an oxymoron as the state of the art in USB DACs is a moving target and price performance continues to improve. The Ayre was/is the leader in its priceclass for asynch USB, the cheaper Wired4sound appears to leads the priceclass just below.
So you have three options - get a computer + USB DAC (probably wired4sound in your price range), get a computer + very good soundcard with S/PDIF out, or get a computer with a USB to S/PDIF converter. The HiFace EVO appears to be the best you can get for a few hundered bucks at the moment. If I liked my current S/PDIF DAC I would personally get the HiFace EVO (as things stand I have the PWD + bridge and could not be happier)
Of course you can get turnkey music server solutions as well but I am not famliar with those.
I have taken a look at the wyred4sound DAC2 it seems like a promising machine. But to just buy one online without every seeing one let alone hearing one is maybe a bit to much of a gamble.
I would prefer:
NAS-->Server (iMac, laptop)--->USB DAC-->integrated amp
Also some DAC are modular, I think this is a smart think. This was you can upgrade the DAC without having to buy a new one. That is one reason why I also like the Pink Faun DAC 2. The Pink Faun DAC standard has 75 Ohm coax and a optical SPDIF input and 2 slots for additional inputs. Pink Faun sell a USB card for one of those slots that still leaves 1 slot open for future options. I was thinking about having a card made for the CEC superlink. This way I can keep using my CEC TL51x CD transport and I can hoop up a laptop to the USB port and in the future I can change those cards again.
But I have no idea how good this DAC is compared to the wyred4sound or a PS audio DAC etc. Sometimes having many options isn't a blessing.