My xc600 used to dart a little, and I simply went to stud boy shaper bars. That fixed it, and it uses a single bar type runner.
We used the dually's on the XCR, and it fixed the darting, but it made the steering a lot more effort. That was no issue to me, but my father did not appreciate the extra effort.
What skis do you have on the 01 600 DLX? The darting got better when I added srx plastic skis to the venture to replace the stock steel skis with skins. I think I can get rid of the rest of the darting with shaper bars and a little more preload on the front shocks.