Scuderia center speaker replacement?

I have the stock stereo in my car, and the center sub speaker is starting to rattle. I've always wanted a better stereo in the car, but don't want to take it away from stock, and I've read mixed reviews on upgrading speakers and adding an inline amp (has this opinion changed?), so I'm thinking of just replacing the functional center speaker.

Has anyone changed out the nav head unit in a scud for a regular 430 head unit? I really dislike it compared to the head unit in my old 360. I miss the preset buttons and the simple reliable rca to headphone jack ipod connection (but, if you used the rca jacks for an amp, you wouldn't be able to operate an iPod ?)

Thanks,
David