Like many here, I'm ready to replace my soundsystem in my 95 E300D. I've been considering putting in a sub under the medical kit as some have described, but have been wondering... has anyone tried to expand the rear speakers? Instead of the 5 1/4"'s that are in there... could you expand the opening to fit 6x9s instead?

I realize this wouldn't be quite the same bass as a 10 or 12" sub in the rear deck, but I hate to lose the space in my trunk... and I don't know how to calculate what size to make the enclosure, etc.

Any feedback would be appreciated. Thanks