This was the first thing I did! I replaced all the interior speakers with 6.5" Kicker speakers and have 5.25" Kicker Marine speakers coming today for the outside. I replaced the deck with a Kenwood unit and have an 8" Kicker Sub coming today as well that will be powered by a 600W Kicker Amp and hidden in the cabinetry for a better sounding system and if it's not already hooked up to the main TV inside, I will hook it up to that as well so we have kinda a surround sound going on in there
The speakers up front were smaller than the 6.5" I believe 5.25" but a quick template and saw took care of that issue.