The wyred 4 sound recovery is a good bit of kit as well - it has improved every DAC I have used one with and if you are interested in playing DSD it has benefits in that many DAC's only accept DSD via USB and not SPDIF. The recovery also benefits from a better PSU so it might be worth getting...

I think jcn3 is referring to the Singxer SU-1 which has a built in PSU.   The F-1 has a better clock than the X-1, there is loads of data here on them here - http://www.head-fi.org/t/803111/xmos-xu208-usb-bridges-the-latest-gen-has-arrived   You can power the F-1 from USB, though it is...