This may be a dead issue anyway. I went to my sevice dept to see about more speakers. It seems that Volvo has used a new wiring system for the new S40 (they say to increase performance and reduce theft). Anyway, even other Volvo model speakers will not work with the new (2004.5 and up) stereo system.
Now I am on a mission...there has to be a way to "up" the system...there is always a way.
Yup, apparently they using some optical fibre link in these babies. Why you want to change the speakers? I feel that for a stock system it has acceptable bordering on quite nice sound. I wanted to put the optional sub woofer into mine and the dealer quoted me a price of around R9500 (South African Rands). I almost passed out. For that price you can kit a much lesser car out very nicely with a system that is going to give you a nice balance between banging and quality.