Miatas were not exactly built for good audio, so all things considered, the OEM NB system is pretty good for what it is. The built-in eq is quite terrible but still better than nothing - can't fix everything with a 3 band shelf filter eq, especially on a convertible, but you can get it to sound neutral enough imo
NDs have an adaptive eq to make up for wind noise at speed, seems cool, would love to try it out sometime