I own both of these cameras, but can’t say I’ve ever used them on a 2-cam shoot. I’m guessing you are talking about a Master shot, and then a tighter shot. If so, I’d use the little camera on the wide shot. If you’re talking about 2 matching telephoto type shots – say a 2 camera interview – then you are more or less asking for trouble, as these cameras really don’t match under viewing with a critical eye.
I think the reason would be the pro-lens vs. the cheaper, fixed lens, and the overall sensitivity of the larger camera vs. the small.
If it’s an important project, you might consider renting a 2nd SDX. If that isn’t in the cards, try to set up the little camera so that it’s lens is wide open to defeat the everything-in-focus look of the DVX100. It’s also been my experince that the little camera can’t handle a lot of contrast – that means you’re better off with “flatter”, less dynamic lighting.
Good luck,
Ken