[I wanted to swap in a 2011 oem HU with HD radio, or one of the Chinese models with the 4.3" screen, as shown in threads on NASIOC and here on the Forester forum] but SVXdc's told me my [2009's steering wheel controls] will not work [and 09 and 11 have a different plug for the aux harness]. I try to get something that oem look maybe i'll try Rosen Nav
I've edited the above quote to explain things more accurately (and so people won't be confused).
Short version: Your 2009's steering wheel buttons won't work on a 2011 OEM HU. Your car's aux harness is different also, but I can build an adapter harness so your aux jack can work.
You only need an ASWC steering wheel interface module when you want to install one of the "name brand" aftermarket head units (Kenwood, Pioneer, Alpine, etc.).
On a Rosen HU, you should be able to connect that directly to your car's SWC wires. If you get one of their made-for-Subaru models, they should include plug-and-play Subaru harnesses to fit your car.
On Rosen's generic double-DIN models, you would need my 20-pin harness (just like you would for a Pioneer, etc.). The only difference is you won't need an ASWC module with the Rosen.
"SWC" is an acronym for "(audio) Steering Wheel Controls."
"ASWC" is Metra's steering wheel interface module.