What I have always loved and yes it is old school and I have had tons of comments on was the old style Pioneer tune speakers. To keep it simple a set in the front and a pair of 6x9s in the rear and your good to go no cutting or buying new panels. And just double sided tape for installation.
Only problem is getting a set. I bought a pair off ebay and the last pair I found at a swap meet for $10 bucks.
They tuck away really nice and are adjustable...everyone had a set of these LOL
AL