One option for upgrade would be to convert the Towers into a pair of Theater Three's. The volume between the Towers and the Three's are close enough and I'm sure your son would appreciate the improvements in the bass. The port will need to be resized. However, whether a 12" driver will fit on your baffle will depend on the location of your internal braces. Also, if you followed Wayne's intructions for baffle cutout on the Towers, you might be short about 1/2" for the compression horns. I know because I've tried.

Gar.