I have had both Polk EX series and Boston Acoustics 3.5CS in there without a problem. If you bend the side tabs up a little, they will sit lower. You can also try bottom mounting them with bolts and nuts (if you can get your hands in there.)
The Polks sat well without mods, because they have no tweeter protrusion, but the Bostons required bending the tabs, but that was it.
I dont have either pair in my car now btw, since I got custom kick panels and went that way instead.
Oh, and the dash covers are very brittle to begin with, they will break there no matter what speakers you have, its just that because there are speakers under there, the dash is thinner and has holes in it. So, after time, they will crack no matter what is in there. Mine cracked there before I even took the stock ones out.
