I've done some research, and clearly the consensus is that Rotella T6 5W-40 is the only oil that should ever be used in any turbocharged subaru ever.
I picked up a few gallon jugs of the stuff, but I'm not having any luck finding quarts. A few different people have suggested Wal-Marts, Tractor Supply, and feed/farm type stores ("Southern States" in my region). I've checked the websites, and they don't have quarts listed, only gallons.
Has Shell stopped packaging quarts of T6, or am I just not looking hard enough?