Todd, if you want to add bags, DEFINITELY remove the stock hard tanks. It only takes 3 or 4 screws to remove.
The first season on my X2, I was running 350lb sacs plumbed in with the stock hard tanks. No matter how you plumb it, it's always a pain to get the sacs and tanks completely empty when you're done, and you can't get very much weight back there anyways.
Last season we removed the hard tanks (4 screws, two hose clamps, that's it), and plumbed in some giant Pro-X sacs. What a world of difference! The wake is better, there's more storage when towing, and it's much easier to empty and fill.