Finally wrapping up my audio upgrade, maybe this info helps you

Tips:

1. Feed your own wires from behind the stereo to the tweeters. It's not hard, you can use a thin stick to tape the wire to and push it through the opening in the dash behind the stereo to each tweeter. This allows you to have your tweeters on your wires and they'll be disconnected from factory wiring. Your front and rear doors will stay connected to factory wiring. Now you have individual control over all 3 sets of speakers.
2. If you're installing your own amp, just use OFC copper. Go to Lowes/Home Depot. It's less than $2/ft for 4awg. Do it right the first time and don't cheap out with CCA wiring.
3. Run your speaker wires to the left under the dash, down the driver side kick panels. Not the right side. Keeps them away from HV lines and the battery on the right. Less potential interference.
4. I suggest something like a Kicker KEYLOC to help you get a flat clean signal to your amp. There's definitely some cleanup to be done to get rid of the factory tuning.
5. The mechanical latch wires for the doors resonate at certain frequencies. It can be annoying. Usually stuff below 400hz gets them vibrating. Really you just have to tape them down everywhere. Still not a perfect solve but it does help.

I've finally settled on a JL Audio VXi600/6i and a NVX VAD10001 to power the subwoofer. I had a custom trunk cover made so if you looked in my trunk right now it looks totally normal. Wouldn't know that under the flooring is my amp setup.

Speakers and why I chose them...
Dash = CDT Audio Unity 8.0: These have good off-axis (ie. not facing directly at you) response which you want given that these are in dash speakers. They are WIDEBAND drivers, not just tweeters. They aren't screechy, they sound great IMO. People say the 7.5 have better off axis response but honestly these sound great and didn't need a ton of EQ to level them out.

Front doors = TM65 mkIV Midbass: Everything I read about them had people praising them with only the best things to say. Honestly I'm not THAT blown away by them but they certainly don't sound bad. It could just be their location that hinders things. And I've tried many crossover points with them. They are JUST good speakers but not worth $300+ for the set IMO (I got mine on sale). But again, might be their location in the door that doesn't allow them to reach full potential.

Rear doors = Alpine S2-S65C: This is the COMPONENT version. There is a coax version as well, which honestly since I'm doing rear fill maybe I should've gone with coax but whatever. This was just on sale, I've had good personal experience with Alpine products in the past and it didn't need to be an exceptional speaker in the rear because I'm just doing rear fill. I have no complaints.

Technicals...

• Measurements were done with a Behringer ECM8000 microphone, calibration file loaded for it, run through an Apple USB-C DAC (sounds silly but it is actually a really clean little adapter).
• I am not a professional anything and I have not had a "professional tune" done. This is all me from trial and error and learning and experimenting and what sounds best to me.
  
• If you're doing a driver-only tune, then by measurement at mic you need to subtract 2.5dB from all driver side speakers. Personally from my listening I felt like -4dB sounded better.
• Crossovers are (currently):
  • Dash - 1,000hz @ 12dB LR
    • Because they are widebands I felt comfortable crossing them this low. And the measured audio response was still fine from them. Will probably settle at 1.2khz though.
  • Front Doors - 80hz @ 24dB LR / 1,000hz @ 12dB LR
    • Could go lower but we have a subwoofer for those, and because the speaker is at our ankle I didn't like more directional frequencies being down there.
  • Rear Doors - 333hz @ 48dB LR / 3,000hz @ 12dB LR
    • Rear doors are doing DIFFERENTIAL REAR FILL. Hence why they are handling this odd frequency range.
  • Sub - 31hz @ 48dB LR / 60hz @ 24dB LR
    • Because people (myself especially) listens to the sub louder than the rest of the components 60hz felt more appropriate. By the time we hit the 80hz crossover of the front doors it blends nicely. Also my high pass filter is 31hz @ 48 because the tuning of my subwoofer is 42hz so 31hz allows me to play max at its tuning frequency and then sharply drop off on lower frequencies which may damage it if they're too loud.
• Timings are (Left/Right, in miliseconds):
  • Dash - 0.78/0
  • Front Doors - 1.21/0.09
  • Rear Doors - 1.95/0.61
    • It's suggested to add extra delay to the rears when doing rear fill but I didn't feel it was necessary. I played with it a bit and just didn't feel a need to add additional delay beyond the standard for distance. Sound stage is still nicely up front.
  • Subwoofer - 0.57
    • Subwoofer is a down firing low profile sub in the trunk area. I set its delay by playing pink noise from it and the front door speakers (setting the sub crossover to 80hz instead of 60hz for this), and then I inverted the polarity of the subwoofer and adjusted timings until I found the greatest dip (cancellation) in my frequency measuring. Then I flipped the polarity back to normal on the sub. That got me perfectly phase aligned sub to front door sound.

 

If I'm being totally honest the effort is not worth the reward.

But I am a project-oriented person and if my brain latches on to something and I go into a 6-12 month rabbit hole of information gathering, testing, and production then so be it. This was not so much "I am an audiophile and i need the best sound" but rather "i'm hypermanic and will dedicate my life for the foreseeable future to learning about and improving this thing that I have fixated on until the dopamine rush from it is gone".

Could you tell the difference in audio between sitting in my car vs a stock gen5? ABSOLUTELY. It is night and day. Even just loading in a blank profile on my DSP with no speaker frequency tuning and no timings, there's a notable difference in audio quality.

Does it matter though in the long run for the general audio experience? Not really.

Add a subwoofer and replace the very muddy sounding dash tweeters with some good widebands and that's enough for the average person to have an improved listening experience without getting deep in the weeds.