Not to be redundant here, but I have much the same question.
(Greetings, by the way. This is my first post, as I plan to pick up a lightly used 2005 Outback XT Ltd. from a dealer tomorrow - my first Subaru)
I also have a Yakima set-up (crossbars and bike mounts) from my old car and am wondering about buying their Lowrider towers to attach to the Outback's side rails, versus mounting what I have on the factory Subaru crossbars via some kind of funky Yakima attachment.
I only plan on putting two bikes on the roof - no funky boxes, skis, canoes, etc. So width of the crossbars and weight-bearing ability aren't really a concern at this point.
If I use the Yakima crossbars, I should probably remove the factory ones, yeah?
Any suggestions would be greatly appreciated. Thanks in advance.