Hi Fi system also has a center speaker. Just no center tweeter. I currently do not have any upgrades beyond disconnecting the center speaker. I mainly listen to podcasts, so audio in the car is not as important to me as it is in my home theater. Once I finish the engine and cosmetic mods I'll start in on the audio.
I plan on getting a JL 600/6 amp, perhaps a separate eq and obviously speakers. I'll most likely go with separates up front and just get the sail panels from somewhere. My current speaker of choice is CDT, but I may go with Focal or Eton. The CDTs are approaching Morel prices and I worry that the JL amp may underpower them a bit too.
CDT AUDIO HD-42 HIGH DEFINITION Model 4" 2-Way Component System
https://www.amazon.com/dp/B00067MR3A..._9juGxbPBJTW2K