Hmmm. So is your head unit also in a round form factor (like the speaker) and mounted on the instrument panel? Prospec shows at least one and maybe two on their site that are. It would only be a guess but I would venture the speakers were OEM quality at best and age in a humid environment has not improved them. 5 1/2 inch speakers are plentiful so replacing those will be easy if you intend to put them back in the same holes. Replacing the head unit, if it's round, will be harder of course but prospec does show a JBL one that "might" be a suitable replacement. I think I would recommend replacing the speakers first and see how they sound. If they sound OK but aren't loud enough, then add an amp between the head and the speakers and see if that helps. If the head unit is [censored] the amp will...amplify that. But you will know if it also needs replacing. So those are my thoughts. There are many more knowledgeable people here to help more than I can. And the suggestion by someone earlier to consider a Bluetooth speaker is a good one if this gets to be too...hard.