IIRC, the 06+ manifold/header does not exit the same "location" as the turbo manifolds. Try looking for a manifold for 06+ Impreza, it'll have the same clearance for the oil pan/oil filter as the Legacy.
If you're just after the sound, you could run with the factory 2005 (non U5/Cali spec) header and fabricate your own cat-delete. You'll need an O2 extension harness due to the relocated bung. I assume you'll also reflash the ECU to turn-off the downstream O2 and and cat-efficiency codes.
If you're just after the sound, you could run with the factory 2005 (non U5/Cali spec) header and fabricate your own cat-delete. You'll need an O2 extension harness due to the relocated bung. I assume you'll also reflash the ECU to turn-off the downstream O2 and and cat-efficiency codes.