4th Gen Audio upgrade Clarification Please

[toyo]

I am wanting to finish upgrading my sound system and have received differing opinions on what I will need.

The details:
I have an 08 LTD JBL Non-Synthesis with NAV. I am keeping the factory NAV/head unit.
I upgraded the door speakers a few months ago using Focal 130 AS. I am looking into using the JL Audio XD700/5v2. I have not settled on an amp yet bt would like to go with JL or Focal.
I am going to change out the Amp and SW next. I have talked to a few shops to gather some knowledge. A few of them are telling me I will need a processor due to the way that the 4R is configured. I have not seen this discussed around here. This is the processor they are saying I need. https://www.crutchfield.com/p_13698100/JL-Audio-FiX-82.html?tp=70736

Has anybody ever had to use a processor like this?

 

[riceandpho]

processor will make the sound better, but integrating new amps to stock radio, a good line output converter is needed, i use the audio control brand alot, if its done right, it can make the stock radio sound good. but why not just get a new radio and not have to deal with extra components? a good pioneer nav will have everything plus a good eq. you can choose to run new speaker wire to the new amp, also the radio just need a few connections, power, ground and switch 12v source. since you will be running new rcas to the amp from the radio.