You lucky bastard

Hitachi 3D woofers are surely one of the best matches for this box. Also some woofers from cheap super jumbos would work fine. The original woofers have volume but there's little to no bass. This box is THE easiest to work on. The other headphone out doesn't have volume control, thats a bit weird, but understandable since there isn't a second volume knob
One could build really fine custom blaster in one of these. They can go for low price too!