I am sure this will bring a lot of giggles and I normally wouldn't advocate it, but I was utterly impressed by the sound quality after fitting some 6x9's I had sitting around into the back of my first 156. (Standard fitment on the 156).
The bass response picked up the entire car and brought it into total harmony. The speakers were Rockford Fosgate "Thump" if I remember rightly and they were about a million times better than any other 6x9 setup I had heard in my "youth". They are probably about 7 years old now, so the likely hood of finding them now is probably nigh on impossible, not sure how current 6x9's compare.
Blow's away the Bose setup in my current car, wish I had remembered to pull them out before I sold the car (out of sight...out of mind).
Current Italian Cars:-
2004 Alfa Romeo GT 2.0 JTS
Previous Italian Cars :-
2003 Maserati 4200 Cambiocorsa
2006 Alfa Brera 2.2 SV JTS
1999 Alfa Romeo 156 2.4 JTD
2005 Alfa Romeo 156 2.0 JTS Veloce
2004 Alfa Romeo GT 1.9 JTD
2001 Alfa Romeo GTV 3.0 V6 Lusso
2002 Alfa Romeo 156 2.0 JTS