I have the base system w/o ANC and just finished installing my infinity reference 6x9's in the front doors. Reading and re-reading this thread until my eyes watered certainly helped and I could not be happier with the results for a fairly low amount of money. I ordered from Crutchfield and their instructions were also extremely helpful especially with the photographing of each step. Took me less than an hour to do both doors. Drivers door came off very easy but I did have to struggle a bit with the passenger side and ended up busting the tip off a clip at the top of the panel. I'll probably open her up to replace it at some point; most people wont notice it I'm sure but I know it'll bug me.
I also replaced my dash 3.5s a few weeks ago with matching (albeit 2016 model year) reference 3.5s that I pulled out of my 300S before I traded it in. Bass response overall is significantly improved, vocals are legible now, and I have noticed no difference in sound level.
Will be doing my back door 6x9s with the JBLs this weekend and running connections for the Rockville RW10CA slim 10" sub I bought returned from the Amazon warehouse for $86. Read a few good reviews on it and it should hopefully fit either underneath the front passenger seat or possibly behind the back seat. Crutchfield provided instructions for removing the back seat so I'm going to tinker with that over the weekend as well and will report back on sound quality once she is all completed.