Here's my scenario
 

OK, I'm about to get my first car which I decided would be a 2002 Nissan Maxima. I've heard the horror stories about the Bose 6-CD changer unit installed in it. I know nothing about car audio (or cars in general really) but what I do know is I have a large collection of MP3s that I love to listen to. Since I can't really afford to get a HD installed right now, I've decided that I should get a MP3 CD unit. My question is: what would be the best unit to get for that and about how much would it cost to get it installed. Do I really need to replace the speakers in the car too? I actually liked to sound of the unit when I test drove it. How much of a difference would new speakers make? I ask this because I really don't like the idea of completely changing the audio system in a car I just bought. Also what about the trip computer and in-dash controls? Will they still work?

Thanks in advance.

If you change just the HU, the sound goes downhill. I am running an Eclipse HU with the stock Blose speakers and it sounds just horrible, no bass at all. I would consider getting a separate sub if you change just the HU. I am going to be changing out all the speakers and subs next month.

I just went and read about converters for older model Maxima HU's to aftermarkets HU's. Are those not prooduced for the 2002 and up Bose models? I looked on Crutchfield.com and none of the converters there fit.

I believe there are converters available. Not sure though.