Hi there Scott,
the calculator won't let you work out what is the best driver. You need to use a design package such as WinISD or Unibox to do that.
Sonosub only uses the physical dimensions of the driver to work out volumes and clearances. It comes with some of the popular drivers included, but you can add your own if it's not on the list. If you don't know the dimensions yet, you can use the built in generic sizes
regards
Collo