Don't put them in the door panels unless you do some reinforcement. On the early S2's anyhow, the weight of the magnets will just pull the door panels off when you swing the doors shut unless something is done to hold them solidly in place. Some people put small speakers in the air vents at either end of the dash....they don't do much as vents anyhow, but you'll need a subwoofer somewhere; and there's always the cut holes in the console sides, which is probably the most practical idea. Another solution is using a Miata Headrest Speaker Retrofit Kit., although I haven't seen anyone on the BB try it yet.
It's what I've been musing about for my car.
It's what I've been musing about for my car.