I had the exact same Outback and carrier. When I purchased my car there were two OEM cross bar options - Thule and Rola. Completely different profiles. But regardless, I had the Rola variety which sat above the roof rails, and I had to take the end caps off these and after measuring where the carrier would sit (2 bolts up front, 1 at back), I then slid the rubber bit out of the bar, cut it where the rack was going to sit, slid the cut rubber back in and tried to mount it.
Turned out the 'T' part was too big for the slot in my Rola's. I went to the closest roof rack shop and they had some thinner T bolts in stock (as in, the top of the 'T', which is the bottom since they're upside down, was too thick). Swapped them over for free, which I wasn't expecting.
Mounted the carrier, put the remaining bits of rubber back in, end caps on, and hey presto.
FWIW the Rola bars, though visibly more streamlined, were noisy as shit. On my next car I got Whispbars, which are completely silent. Plus the rubber bit in the groove is a tube that expands from inside the bar, so you just push the carrier t-bolts in over the top of this - no cutting.
In the end, I ditched all of it and got one of George's carriers, which was probably over-engineered for my 90% on-road driving. But there's no denying the quality and strength of those things, and a rear towbar carrier was infinitely easier and better than roof mount. Better economy and less bugs on bike on long trips. No low garage/carpark/drive-thru issues.
But I'm a lazy bastard - in the end I just bought a truck and a tailgate pad. Which is the best carrier system I've had so far.