Short answer, yes you can swap out the speakers. Dash is easy, doors are a little more involved (remove door panel, deactivate the ANC). Here’s what I would do @KorkSo, sorry if this is basic or a repost but just want to be sure. I have the 8.4 lcd in a big horn but the basic 6 speaker sounds system (i believe). Can i replace the corner dash speakers with 3.5 speakers and the four doors with 6x9? I believe i have ANC. Do i need anything other than the speakers and a wiring harness for each? I have i thing coming out of the center dash speaker and don’t need to replace anything there, correct? Crutchfield says something about the ohms and that volume will be lower and so, I’ll admit, I’m thoroughly confused here. Any guidance would be very much appreciated!
1 - Confirm which system you have... does the center dash cover say Alpine, or do you have speakers in the headliner? If not, and you have a V8 Hemi, then yep you have 6 speaker base with ANC.
2 - Determine what’s your goal, budget, and how much time do you want to spend? How comfortable are you ripping the door panels off, or removing/cutting the wires going to the ANC/amp module? For better sound your options range from simply finding better music sources (super easy), replace 3.5s only (easy), replace 3.5s+6x9s and deactivate the ANC (harder, this is what I did), or replace the amp and speakers + add a sub (like @WRH did, hardest).
3 - You can just replace the 3.5” dash speakers for better highs, super easy cheap option. Some use JBLs, I used JL Audio (with trimming and bass blockers). Lots of options but yes if you want balanced sound volume look at the impedance (ohms) and sensitivity (dB) of your replacement speakers... or trust someone else’s opinion/recommendation on speakers.
4 - You can also replace all 6 speakers, just pay attention to not exceed the max depth of the magnet or height of the tweeter. You don’t want interference with the window mechanism or the door panel. Perhaps my install posts will help, did you read them already? It’s a series of posts so you have to follow my links to complete the story. Good luck!