Thought I'd post this to help anyone else who might be having the same problem.
Just got my FiiO E17 today, plugged it into my laptop (Lenovo W510), and I couldn't get Foobar to recognize it as a valid output device. After plugging it in and out a few times and trying the beta drivers, it started to generate a "Blue Screen of Death" on my laptop. Then it started to do this every time I plugged it in. I uninstalled all of the extra drivers, but it would alternate between not detecting as a valid output device, or just crashing my computer.
I went through the minidumps generated by the BSOD, and the problem was related to the nusb3xhc.sys driver for the USB 3.0 Root Hub, and USB 3.0 Host Controller. The DMP files showed BAD_POOL_CALLER or SYSTEM_SERVICE_EXCEPTION at VISTA_DRIVER_FAULT.
I went into Device Manager, and my USB 3.0 Host Controller was showing up as "NEC Electronics USB 3.0 Host Controller". The nusb3xhc.sys file version was from 2009.
I downloaded the newest version available from Lenovo, but it was only from 2010, and even after that, it would still BSOD when I plugged in the E17.
I did a bit of hunting on crashes related to this file, and found this post which describes a similar problem, and that the drivers may not be under NEC anymore but Renesas.
So I hunted down a newer version of the driver here, which is 220.127.116.11 (15 Mar 2011), downloadable from HP's site, and installed it. Now my USB 3.0 components show as Renesas instead of NEC, and the FiiO E17 worked perfectly, detected as "SPDIF OUT (FiiO USB DAC-E17)"