Do I need a Signal Processor?
 

2011 XLT Supercrew with fac stereo. No fac upgrade or sub.
I have a 4 channel amp for the doors and a stereo (2 channel) amp for two subs.
I've been reading good things about this
AudioControl LC7i

and this

Kicker KX3

Try it without it first. I had the same setup and changing out the door speakers and adding a sub made a huge difference.

Sorry, didn't mention door speakers are Infinity Reference.
I expect a huge difference. I want it to sound nice, not just upgraded.

I debated what you are thinking and decided to go without for now. I just did 6,5" Polk components in front and 5x7's in back with a 10" sub. I am just using the amplifiers processing along with the crossovers for the components up front and I feel the sound quality is greatly upgraded. No extra processing required. I'd say just have them install it without and like someone else mentioned, if you wanted to add one later it would be very easy to do yourself.

I agree - you might find yourself saving several hundred dollars and you would never know what you're missing.

I went with an amp, dual FoxBox, subs, new door speakers and a 4-channel LOC. The difference is beyond my expectation. I had fully expected that I would be adding a processor but I have no intention to get one now.