Well a 2" deep speaker would probably fit in there. The ones I had put in were 5" across, and almost 2" deep. I was eyeballing a pair of Polk Audio 5.25" speakers, which would have fit width wise, but they were super deep (they were extra high-quality speakers and they had a really beefy magnet) and they wouldn't have fit depth wise.Its rather simple, the plastics need to be lifted off from the sill, not a big or hard thing to do.
But I had a little fuckup already, I bought 6,5" coaxials rather than 5" to the back doors. Maybe Ill leave the rear doors alone and put the coaxials in the parcel shelf.
Or how did it seem, is there adequate space for about 2 inch deep 6,5" coaxials in the rear doors? I can order a 6,5" MDF spacer if there is a flat surface it mounts into? I can cut the plastics no problem, they get hidden anyways.
I'm not sure where exactly you could start with this, the aftermarket adapter will not fit speakers that large, with a custom made bracket, anything would be possible. With a ghetto-rigged bracket, anything is still possible, although it wouldn't be as pretty