So I just bought a 2003 A4 3.0 Quattro. UNfortunately, no Bose.

So I have to replace the head unit with a GPS/bluetooth/stereo deal.

But I am wondering how many speakers I must replace. I know there are two speakers in each door -- a woofer and a tweeter. (Although I'm not sure if the "woofer" is actually a two-way or not.) Also, in the trunk there seems to be a metal piece made to hold two round (sub-woofer?) speakers -- but there's only one speaker there. Is this a factory lousy sub-woofer?

Also there's a grill on top of the dash itself. Does this house another speaker?

I'm thinking of only replacing the four speakers in the front doors, and seeing how that sounds.

Any answers/advice anybody?

Thanks so much!