I would probably take the opportunity to ditch the Touch. I know its hard. I have the Transporter, and have moved on for some time now. Squeezebox Server has been abandoned, and at this point there are much better interfaces out there for PC or MAC. The PC/MAC is a much better basis for the USB DAC's of today (high res. DSD, etc.). I dont know about the Touch over USB, but I know that my PC over USB sounds much better than my Transported did over SPDIF.
Well, that's something I've been thinking long and hard about. I'm really pretty clueless about this stuff so my head is swimming with different options, such as NAS>modified Mac Mini>DAC vs Vortexbox>SoTM SMS-100 Mini Server>DAC vs a PC based setup like a CAPS computer>DAC, as designed by Chris at computeraudiophile.com.
But I'm most excited about the Auralic Aries coming out soon. Seems to be custom made for someone who wants to use a USB DAC in their setup. It has a iOS/Android controller that looks more elegant than Logitech Media Server, which works well but isn't an intuitive or attractive interface if you ask me. The Aries is basically a custom audio computer purely designed for high quality playback.