Multichannel digital recording in Mac OS

Hey guys, I know a few people with some digital recording experience hang out here and I wanted to ask for some help understanding something. I would like to make some live multitrack recordings of my band. Nothing fancy, I would just like to be able to separate things out instead of recording the stereo out from the board to Garage Band. We got a Yamaha MG166CX mixing board with a USB interface that came with Cubase AI 4. It seems possible to record multiple steams (or channels, I don’t know the terms) at once by setting up the Yamaha as a “VST Audio System” device in Cubase. I would much prefer to be able to use GarageBand as the recording software, but I don’t see any way to make GarageBand recognize the Yamaha as anything but USB Audio, which is just stereo.
So my guess as to how this works is that Cubase has a driver system that can talk to the Yamaha in a way that pulls multiple channels over the wire, but GarageBand doesn’t. Is that the case? Is there a way to make the Yamaha do what I want in GarageBand? I guess I could start to try to learn Cubase, but GarageBand is so friendly! ?