The new model Outback (05+) has integrated climate controls in the dash with the factory radio and cannot be separated. I believe that some standard Legacy models have separate climate controls, but most Outbacks will have the integrated stereo. The one place to put the Empeg is in the top accessory pocket, as shown in Ezekiel's post. It doesn't fit perfectly, and some supports have to be cut in the dash in order to make the opening deep enough to fit the sled. A good way to integrate with the factory stereo would be with a JL Cleansweep which would give you line outs from the factory stereo and an aux in for the Empeg. You would have to mount a separate volume control for the Cleansweep.

You would also be able to buy a factory fit sub from JL, their Stealthbox looks like it works well for the newer Outbacks (I had to make my own for a 2000).