This is the process of setting up the CO1U to work in Logic. This will only work in OSX 10.4 or later.
10.3 and earlier versions don’t have this facility.
1 Open Audio MIDI Setup (from the Applications/Utilities folder)
2 Go to the Audio Menu - Open Aggregate Device Editor ⇧⌘A
3 Click on the + button to create a new device
4 It's a good idea to rename it (double click on Aggregate Device in the list and enter the new name eg. CO1U)
5 The list at the bottom of the window will show all the audio devices connected to the computer. Select the ones you want the device to use by checking the “use” button. For instance, if you only have a CO1U connected you will need to check CO1U and Built-in Audio. Check the clock button on one of the devices, not the CO1U.
6 Click Done

And that’s it. The device will then appear in Logic under Audio Hardware and Drivers as an available I/O.