Bandwidth is the freq range that you are going to boost when using the bass boost.
Im not sure what freq their bass boost inhances, but Im going to use 35hz for example.
A wider bandwidth will boost from say 30hz - 40hz. Where as a narrow bandwidth would pretty much just boost 35hz.
Phase - this is for changing the way the woofer hits, and used in strapping amps together. Neither of which I think your doing so leave it at 0.
Sub sonic filter - This pretty much limits how low of hz the amp will play/amplify. If your using a sealed box you really dont need to use the subsonic filter, however in a port box you want to adjust the SSF to a few hz below your box tuning (or generally 29-33 hz)