Just bought a brand new Cambridge Audio DacMagic 100, and I'm really pleased with it.
The only slight foible with it was that, out of the box on Mac OS X, it defaults to USB 1.0, rather than USB 2.0. This means that the maximum sample rate supported by default is 96kHz, rather than the advertised maximum of 192kHz.
The simple way to fix it (as found in the depths of the online PDF manual) is found on page 14:
Switching between USB Class 1 and USB Class 2 operation
Your DacMagic 100 will come set to driverless USB Audio Class 1.0 by default, but it can be configured to run in either USB Class Audio 1.0 or 2.0 mode. To change USB Class, press & hold the Source button while bringing the unit out of standby. One of the digital input source LEDs will illuminate to indicate the current USB setting: Digital 1 represents USB Audio Class 1.0, likewise Digital 2 is USB Audio Class 2.0.
Simple fix, but not otherwise too well-documented on the internet. The DacMagic 100 should now have the 192kHz light illuminated, and it should show up as using USB 2 in System Information, and Audio MIDI Setup; set the DacMagic as the default output device and you're sorted. I can't think why they thought it was a good idea to default to the lower quality, unless there were compatibility issues: I think all computers sold within the last 15 years have USB 2.0 or higher.