man i think i missed out on the variable speed fans lmao after 4 years without searching new computers and building them im out dated in techno hahahahaa

if you're doing a design like that, then use a class d amp as they generate a lot less heat, set up the fans as the guys mentioned in a push/pull configuration, and make sure the sub box is very well braced (try and locate the amp above a brace), as this will prevent the amp from flexing and breaking internal components.

I like your design, has given me an idea for my design im about to build :)