[KevinH1990]

To answer your specific question, a good head unit can power the dash and door speakers. The issue you will need to address is that the speakers in the doors are not full range speakers. They are designed to transmit low-range sound, but they aren't subwoofers. When I upgraded my sound system, I replaced the door speakers with low-range components and powered them from the subwoofer output of my head unit using an amplifier. If you put full-range speakers in the doors, they would probably sound okays using the rear speaker output of the head unit. You can see how I addressed the door speaker issue in this thread. https://986forum.com/forums/boxster-general-discussions/79558-door-speaker-recommendations.html

Another complicating factor for your car is that you have the MOST audio interface. (MOST is an acronym for Media Oriented Systems Transport.) This is a fiber optic system that will require special attention when you upgrade your system.

I don't have this system in my car, and I don't have any hands-on experience with it. There were adapters on the market that might make your job a bit easier when you upgrade if they are still available. I suggest that when you search for instructions on the work that you make sure the guidance applies to the MOST system. You may want to consider a company such as Crutchfield that provides vehicle-specific support with their products.

The speakers in my car without the Bose system were of poor quality. I found that replacing the speakers with better components and adding speakers to the rear storage compartment made a significant difference in the sound quality.

I also recommend that you consider a double-DIN unit with Apple CarPlay or Android Audio. It makes the car feel more contemporary. I installed the double-DIN unit in my Boxster before Apple CarPlay was available. I have Apple CarPlay in another car and I will add it to the Boxster if my current unit ever needs replacement.

Good luck with your project.