I believe I have seen some threads about replacing the head unit, but can't find them.
The roadmasters with electronic climate control use circuitry in the audio head unit to dim the climate control. When you go to an aftermarket unit your climate control is on full daytime brightness all the time, which drove me nuts.
Several 90's Buick models had the same double din head unit. I pulled one from a 98 Park Avenue, it seems to have a better CD player. I have seen some Buicks with the same kind of head unit and steering wheel as ours with controls on the steering wheel - if you would consider that any kind of an upgrade.
Here is a thread about front door speakers.
05 magnum rt with srt8 300 front
95 dcm wb4 rmw funeral car from fred - sold
93 white woody rmw - sold