'05 Excursion Rear Speakers

[SnackMasterX]

Hello,

I have been getting work done on my excursion at the local professional car audio shop and needed to verify that I heard something correctly at the store before moving forward with purchasing speakers. My brother works for HP and gets insane discounts on JLB or Infinity car products so I was thinking of going with infinity for door speakers and JBL for amps however the main thing I am wondering is how the back speakers are connected (in series or in parallel), also the ohm rating of the speakers. I heard something about there being a module the back speakers are connected to and not sure the rating on the speakers themselves or how they are connected however from what i understand this module keeps them running at 4 ohms, now i'm not sure if that means that the speakers themselves run at 4 ohms or if it means if I hook the speakers up to an amp (through the factory wires from behind the head unit) the amp would be outputting at a 4 ohm load. From experience infinity speakers are freaking amazing and I would love to have them all around and if there is such a module for the back speakers I'm wondering how it would end up working out when I connect infinity speakers. For anyone who may not be aware the infinity speakers are 2 ohms which is the reason for this post and as far as I'm aware the factory speakers are 4 ohm.

Thanks in Advance!