Mac Mini doesn't "see" Peachtree Grand

I have a Mac Mini, circa 2010, running the latest OS. When I plug the USB cable in between it and the Peachtree Grand Pre X-1, the PT doesn't appear as a device when looking at the audio output options on the Mac. I tried the same cable plugged into my Macbook Pro and the PT shows up there just fine.

Any ideas why the Mini wouldn't recognize it? I tried multiple reboots and power recycles with no luck.