I originally thought the factory speakers were inherently terrible. All I ever got from them was shrieking highs/mids with absolutely zero bass.
Honestly, the speaker on my Samsung Galaxy S10 sounded better. It turns out, the factory Alpine INE-W960 HU must not have been communicating properly with the factory amp and sub, because all of those issues were solved after installing a new head unit.
Besides the sound issues, I have been really bothered by the fact that this car does not have a Temperature gauge. I live in Texas and our summers hit 100 degrees F, and my biggest concern is how hot the engine and coolant get since this is my first mid engine car.
With these things in mind, I decided to install an Android head unit to address them. There are a ton out there, but I chose the Atoto A6 Pro for $259 on Amazon. Post install, I'm glad to report that the RCA jacks for the backup camera/amplifier/subwoofer plug up directly to it just like on the stock Alpine radio and all work properly.
Miraculously, after installing the new head unit, the factory amp and subwoofer are working properly now! There is deep bass coming from the sub as well as balanced mids again! It sounds like a totally acceptable OEM radio, and I now have zero desire to replace any of the speakers. For whatever reason, even though the factory amp and sub were plugged in properly on the Alpine unit, they never seemed to be on or working. On top of that, this HU also gives me access to essentially any app on the Google PlayStore (Google Maps, Spotify, Netflix, Youtube, Torque, etc). I use an app called Tasker which turns on WiFi tethering on my phone automatically so that there is always internet for Spotify, Maps, Youtube, Netflix, etc while I'm in the car.
Lastly, for car status monitoring, I also bought the Veepeak Mini Bluetooth OBD2 reader from Amazon for $11. With it plugged in and the Torque app running on the radio, I can get access to a real-time Coolant temp gauge, boost gauge, intake temp, etc. After a few days of spirited driving in the Texas heat using this, I can report that the coolant temperature in my Evora 400 never rose above 190 degrees. It seems that the cooling system in these cars is up to the challenge, and I no longer have to rely on a blue light, no light, or red light on the dash to tell me if the car is overheating. As for the boost/vacuum gauge, it seems to max out at ~18in/hg (~9lbs) of boost from the supercharger at WOT.
Overall, this install is no more difficult than in my old Honda Civic, with the hardest part being the need to modify the plastic brackets and bezel with a dremmel for fitment. If anyone else out there is disappointed by the OEM sound system or their factory amp and sub do not seem to be working properly, try changing the head unit out first to rule it out. It might be easier than replacing the amp in the backseat.