Im honestly going to have to disagree with all of you when your saying OEM is crap.
Wile original basic sterio systems may sound like garbage the newer systems being put in todays cars are anything but.
Look at the Bose Audio system being put into new Acuras. The Boston Acoustics system in new Chrysler products, or the Harmon/Kardon found in Lexus. Your going to tell me those OEM speakers are crap? In my opinion that OEM "crap" will always sound 100% better than aftermarket unless you go along the lines of MB Quart or Bostons high end line. Now back to the actual subject.
If you do not have the Infiniti amp already in place do not waste the money on the Chrysler/Infiniti Spatial Audio system speakers. The 6 1/2s located in the front are for base only, your not going to get any audio out of them besides thuds. Compair them to subwoofers if youd like.
Now if you do have the Spatial Audio system already in place dont waste the mass ammound of money on aftermarket crap. You'll find that the originals will be just as good and sound alot better with your system, plus there will be no need to wire your car, dick around with an amp, a line level imput, or aftermarket HU.
In short, if you have the original factor Infiniti Spatial Audio system in the car go with the factory, its cheaper and requires alot less bull shit.
If you dont, then have at the aftermarket.