I think if you fold down the rear seat you'd have room for a snowboard. As far as exhaust I like my N1 catback...quiet at idle and moderate throttle and a good loud tone a WOT. I'm not sure about the stock sound system though because I've never had the stock sytem.
For more about the different exhaust systems and such...check out
www.dsmtuners.com and look at the catalog and the tuning guide, that's where I've learned the little that I know.