Since I use Final Cut Pro and not iMovie I can only tell you how I get audio from the XL2 in that way, but perhaps there’s a setting within iMovie that will accomplish the same thing. First of all you probably have to capture your video and the first 2 channels of audio at the same time. Then you need to make a second pass and capture the second 2 audio channels without capturing the video a second time. This is something you’ll have to find in the iMovie preferences somewhere. In FCP you have to do it this way and I’m assuming that iMovie won’t be any different.
Hope this helps.
– Don
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