I listen to alot of classical, and have Polk Audio's in the rear with a powered SAS Bazoka Tube subwoofer, and a matching slave tube in the trunk:
http://www.sasbazooka.com/productAutoAmplifiedBTsEL.asp?id=9
Sounds great to me. I love good Bach organ music, and that really shows a speakers' weaknesses. Good bass reproduction is a must
I'm still using the factory speaker up front for now. Some opera, especially a good soprano, sometimes sounds a bit thin, so I need to replace the fronts. I'm thinking i need a mid-bass too, to fill in better. Just need to figure out where to put it. Don't want all the bass in the rear.