I went to a professional audio installer for this very reason. They wanted to put a subwoofer box behind the passenger seat making it so that there is even less leg room than what a stock Crossfire has. I am 5-10 and I have to drive with the seat all the way back and that still is not enough.

Or they suggested taking a saw to the rear bulkhead and making the openings larger. That was the least objectional idea.

Or putting a sub box in the trunk and making it boom through the rear bulkhead. The trunk space in a roadster with the top down is very limited as it is.

There has to be a better way.