The PowerWave is full of features that separate it from some of the other USB audio devices on the market. To start with, it includes a 10-watt-per-channel amplifier and comes with Griffin's $25 ProSpeaker Breakout Cable, so you can connect standard stereo speakers -- not the cheap powered kind hooked up to so many Macs -- directly to the unit and get great sound. You can also connect Apple's Pro Speakers to the PowerWave, since Griffin uses the same connector on the PowerWave that Apple uses on select iMacs and desktop Macs.
For sound input and output, the PowerWave has stereo RCA jacks and minijack ports and includes the cables necessary to connect the unit to your stereo or iPod...
This thing is a cross between a stero amplifier and a digital/audio converter. It's key selling points are:
1. Connect digital speakers to a computer that lacks a digital speaker output jack (USB to computer, digital optical to speakers). (May need additional cable from Griffin, they don't provide enough detail on their web site).
2. Digitize analog input, especially LPs. (Warning -- this is tedious work and high quality results require specialized equipment that audiophile geeks typically lease -- Macintouch had a great discussion on this.)
3. Hook up stereo speakers directly to a computer (USB from computer to PowerWave, PowerWave RCA jacks to included breakout cable to speaker wires).