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.