Hello Kat and welcome to the Cow Audio Forum.
ART makes some nice things, but this appears to be one made for a low price point.
If you are using the AC adaptor, try not using it. That will eliminate a problem Jordan refers to.
From your explanation (and thanks so much for the details) it sounds like the problems are in (or caused by) the device. Points to you for navigating the sound control preferences. Have you also looked at the Audio/MIDI utility in the Mac Utilities folder?
As to Firewire, or not, USB, itself, can be cantankerous, but you're right, an over-extended FW bus can be as well.
Sound Devices makes a much more expensive USB interface that is exceptionally well-built.
http://www.sounddevices.com/products/usbpremaster.htm
At $549 from B&H, it's a LOT more expensive, but it does a lot more and is built like a tank.
Please let us know how you make out.
Regards,
Ty Ford
Want better production audio?:
Ty Ford's Audio Bootcamp Field Guide
