I did a search on this here and at Nastysock, and couldn't find anything, though I feel like I've seen this somewhere before.
My current WRX has the crummy OEM sub under the passenger seat. I still have the OEM sub that came with my first WRX. I was thinking of trying to make them both work; should just be a matter of getting power to the added sub and giving it the same speaker inputs as my current one.
Has anyone done this?