Apogee Duet Firewire Issues with Snow Leopard

I'm having trouble with my Duet driver and I can't pinpoint the cause. I use a Mac Pro Quad 2.66 8 GB with 2 internal 1TB drives, running Snow Leopard. My Duet functioned fine until the middle of March when I moved across the United States. Before I moved I cloned the OS drive (Snow Leopard 10.6.7) using Carbon Copy Cloner.

A few days ago, I got around to powering up my Mac. My Duet didn't work. I booted from the clone, and it still didn't work e.g. my computer recognized it, sometimes it received a sgnal, sometimes not. I use a mixer, power amp, and stereo external monitors. When there was a signal, it sounded distorted, though not weak. Sometime I heard only the left signal, though the LED's on the face of the Duet registered both L and R channels.

Eventually there'd be silence, and then the signal would start to out of my Mac's built-in speakers. The Duet no longer appeared as an option in System Preferences or Audio/MIDI Setup.

After I'd install the Duet software, my Mac would frequently get hung up, and the spinning beachball would appear.

I uninstalled, than reinstalled the "Duet_Update_Sept09" from the Apogee site. The same. I upgraded to 10.6.8. The same. I even reset the PRAM.

I decided to do a clean install of Snow Leopard, then installed the drivers. Much futzing around as above. The same.

By the way, I also use an iMac running 10.6.7. I tried the Duet with that machine and it worked flawlessly.

Any suggestions? I suspect it's a hardware issue. Do I maybe need a new Mac?

Thanks for your time.