psychobabble,
I know Mazda had a factory turbo Miata in the Australian market. I also know that Mazdaspeed (their factory tuner division) is introducing a turbo Protege 5 but I haven't heard of an upcoming turbo Miata for the American market. The standard Miata 1.8 could easily handle 180 hp without having Mazda worry about the warranty so it is a possibility.
Sushi,
You can still find relatively decent amps that aren't too expensive. I'd go for a true 4X50. I've got two old Rockford amps in my Miata. A 4X50 and a 2X100 on my stock alternator. A 4X50 won't tax your stock alternator.
Even though Rockford isn't as good as they used to be, they are still good amps. I'd go with them, MTX or JBL for not too expensive, good power amps. You'll probably pay 200-250 for a good 4X50 amp.
Frank
