I went on crutchfield and Bestbuy and used their fitment guide. According to those there are only a few 6.5" speakers that fit. Are they accurate?

 

Go to Lucid Automotive site. He specializes in speakers that "fit" the S2000. Even if you don't buy from him, you can see what there is. Some are drop in and some require an adaptor kit.

 

with only slight modifications you can make most speakers fit

 

What sort of modifications?

 

Cutting out the speaker baskets and using an adaptor ring.

 

clearance issues... the speakers can be too deep (get in the way of the window), too large (for protective baffle/basket), and/or doesnt screw to stock adaptor (though they should come with some custom adaptor rings)

 

See the link in my sig line... I have a diagram with useful dimensions.