I had installs in my previous cars. I ran a sony install first and then I went to alpine and JL audio. I finished up with DLS stuff with JL audio subs. Oh, and 125 db.
I have heard some proper installs and believe me, if you want bone trembling bass then 12s will provide it but if you want all round usability and just good sound then 1 10" quality sub will be the best option.
For just driving about the bose system is fine, can lack bass but it's alright.
If I was to upgrade it it would be with high quality gear and loads of dynamat. You are looking at serious weight!
Cheap stuff is normally junk - get the good stuff, you'll really appreciate the difference