I dont believe the racks are the same. the Outback uses a clamp on foot, whereas the Liberty needs a foot that bolts into the factory rail after removing a little cover that covers the threaded holes...
that being said (and I haven't explored this too far) if you can get the foot pad from this Thule kit
you MAY be able to clamp Outback bars to it...
I'm looking at how I can use the same bars between our MY04 Forester and MY07 Liberty, and thus far looks like I have to buy a different foot kit...
Your options from what I can tell are:
http://www.thule.com.auhttp://www.rhinorack.com.auhttp://www.whispbar.com.au (claim to be the most fuel efficient, and quietest roof rack on the market)
http://www.rola.com.auI tend to be a fan of Thule, as I've been using them for years, across about 6 cars, and my accessories all still fit... the Whispbar, which are ProRack, sold at Autobarn seem ok, but their fitting instructions are a bastard to follow, and I don't know about accessory compatibility. Rhinorack fits most Thule accessories without adapters, and Rola needs an adapter for SOME Thule accessories...