So, my SPS-690As finally came in (lets see, its been a month now for shipping) and got em all wired in and hooked up, just to notice that no, aftermarket speakers do not fit. Dont get me wrong, Im not gonna have to grind anything, its just that the stock speakers use three screws and aftermarkets use four. Sounds like an MDF fabrication project to me (
using this guys ideas)
BUT i came across a few oddities. For one..

Is this a sub?

Why, i do believe so. Strange. Anyone want to buy it off me?
Dont know what this is or why its there, but it has the same female terminal that the speakers in front, in back, and the tweeters all had.. Weird..

Its behind the corner foam in back, on both sides of the passenger bench.

So, now to Home Depot to get me some MDF. Hope I cut good...