Plug it it. Go to your Apple menu and System Preferences. Click on Sound then Output. Select the USB audio device. There's a menu extra you can get called Soundsource that makes it easier by putting all the options in your menu bar.
yep these guys have it covered; in your audio/midi setup probably better than your system prefs you should be able to select it as a usb sound source. then you may have to also select it in your audio applications as source if you have more than 1 connected. Itunes will use it automatically if it is selected in the audio/midi prefs though. the system prefs will setup audio for applications beeps etc. but if you want to use it for audio apps including itunes then audio/midi is your best bet.
the path is .....your disk/applications/utilities/audio midi setup. this way you can set it up so the D3 plays music etc. and your card on the motherboard plays the system allerts so you dont get blasted whenever an email or unexpected sound on the internet happens. also you can set-up whats called an aggregate device that combines all of your inputs and outputs from all the devices including the D3 and the onboard chipset; so you can for example use your optical out connected to a dolby receiver for movies and the D3 for itunes without having to go into the system prefs and change it each time.
Let me see...
1. Hook up the iBasse D3 to the Mac (not MAC), using the USB cable.
2. Open 'System Preferences", navigate to 'Sound' -> 'Output', then change output device to "USB Audio Device" (or something similar).