This should be obvious (I think), but just make sure that no matter what you do, you don't mix in an L and R from the SBD into the M and S channels of your AUD in real-time, unless you've decoded the M-S into L-R on the fly first. Otherwise, you'll be mixing apples and oranges, and you'll be screwed. If you can record the four channels seperately from one another, then this won't be an issue.