It will work on a normal Miata setup, but you will be left with an extra plug on the bottom piece that has not matching harness in the wire loom. This would be for the seat thumpers that are not on a Miata that did not come with this stereo.
Additionally, another item that came in Miatas with this stereo option were door tweeters running from separate crossovers located in the doors.
Unless you have the entire setup, I would just go aftermarket.
The silver MSSS1 radios are very temperamental and rarely completely work.