Yes I plan on doing a stereo upgrade this winter too. My boat is an '04 as well and I upgraded the head unit the week after I got it. I want to put in new 6X9 speakers, a modern amp(s) and a 10" sub or 2 this winter.
I have two 10" subs in the cuddy and 10 6x9's. Could have spent more but it's plenty for us