Yes, hi.
I'll do what I can, to cover most info.
For the money, and wanting factory locations, that jbl set is hard to beat.
Jbl is made by Harman, same company that makes infinity. Here is the link, Amazon also has extra reviews,
http://www.sonicelectronix.com/item...dium=paid&utm_campaign=criteo&utm_content=JBL
you can spend $100 raise the stage get some extra midbass, or you can spend up to $1000, on a set from hertz, like the MLK line, or a Morel brand with the Elates model, but having larger tweeters, it makes it difficult to place them on factory locations, and the installation needs sound deadening on the doors, maybe close inner door openings to get the most benefit from an expensive set, besides way more power. It does not cost too much to improve factory sound, if you want to take it to a much better level then, there are other options.
Several users here have used the factory sub, with a better amplifier, with acceptable good results, it is hard to know until you try it or know if you are willing to spend more for better or more bass.
If factory locations are important, it may be worth trying the OEM sub, Currently there are not any shallow aftermarket subs that can be placed in factory locations, unless fiberglass or .5" thick MDF wood is used to build a box, maybe some pioneer models and Dayton at parts express are the only choices for boxes that may fit behind the seat.
If you are willing to utilize some space under the rear seat, you can go with
http://www.crutchfield.com/p_500SBRS84/Alpine-SBR-S8-4.html?search=alpine_8_box&skipvs=T
Maybe sonic will also have it . It's a ported 8" and just seats under the rear seat, with minor strapping needed, maybe with an extra piece of wood, the seat posts can hold it and keep the box from moving or flipping, JL also makes almost an identical box version that just fits there.
Also as the sub and boxes get bigger, more power or an extra amp may be needed to get the most from them.
I share the same thoughts as Optimus on the relays use.