From what I can tell, the clamps from Yak may work but the range of positioning will be very limited. The clamp needs to wrap around the roof rail for it to work, and our Lambda's rails offer only one very short section in the middle of the rail to clamp.
I had Yaks on my old Forester back in college, they were hella noisy on the highway. I made a decision to stick with factory racks after that experience.
Depending on what you plan to carrying on top, factory racks works over 95% of the time and usually rated to carry more load than Yaks or Thules.
I spoke with a Thule rep at a local dealer/installer of roof boxes and racks... and they said that i should get the factory cross rails and mount the rack, box etc.. using those. Apparantly, the Thule rails will not work or they do not provide you any range of motion (front to back I think) if you do use them vs. the factory ones.