adding a sub and amp is the easy part. Deciding on what amp and sub you want is the hard part. All you'll need is an adapter from the bose to give you rca outputs. then hook that up to your amp and then hook up your subs. Depending on what box you go for the sub, will depend on what sub you will need. Also adding an ipod to my stock bose helped the stock system out a ton as well. The ipod acts as an amplifier itself and gives the bose a boosted cleaner signal, at least it seems that way.
you'll need a 4 gauge amp witing kit from somewhere like
www.knukonceptz.com.
Just do some searches, and you'll see a ton of stuff. at first i was just going to do a simple sub and amp install, but then i got into sound deadning as well and that turned into a project into itself. Good luck and let us know if you have any more questions. i have to find the link for the adapter....
here is the link to my old thread...
http://forums.corvetteforum.com/show...ac&forum_id=20
i got a lot of great info from these guys, take a quick read. it was basically a FAQ in itself