Need guidence with a new install.

My wife has a '94 Ford Explorer 2dr.  I want to surprise her for her birthday and put a new system in.  Here is where I need help.  I have been told that this truck has a factory amp that needs to be bypassed.  Ok, so I need to buy a harness for that.  Is there anything that needs to be done with the amp afterwards?  There isn't a lot of room in this truck so I can't put a box inside.  Are there products that will allow my to put I good, clear, loud system in?  I'm guessing I would need an amp, but what about the speakers?  Do they make speakers are a little more robust so they can push out a good range of sound?  She doesn't listen to any bass thumping music, but she does like good, clean, clear sound and the ability to play it loud at times.  I don't know if this matters but she wants a CD/MP3 player that works with XM.

Any help will be very appreciated.

Thanks a lot.

I upgraded the stereo in my '94 and it was pretty easy to do.  Go to crutchfield.com and enter in your vehicle info.  All the products that fit the car will be displayed.  I ordered the following from Crutchfield: Alpine 7893 (CD/MP3 player) and 2 pairs of the Polk EX series 6x8 speakers.  The Alpine has a very powerful internal amp (60x4 max.) and puts super clean sound.  The Polks are great for the explorer b/c they have a rotating shield on the tweeter that can be positioned to emit sound upward as opposed to outward.  This is helpful considering how low the speakers sit in the door of an explorer.  Ordering from Crutchfield is recommended b/c the will provide the following for free: vehicle specific instructions on the head unit and speaker install, a head unit mounting kit (if required), OEM speaker wire adapters (no need to splice) and an OEM amplifier bypass wiring harness.

No need to throw in an aftermarket amp unless you want to power a sub.

Good luck.