Speaker sizes are:
4" in doors (mid-bass); you can fit 6.5s though.
1" tweets in the "sails"
3"(?) full range in the rear (I think you can fit 5.25s though).
There were many stereo options available in the MR2. The premium stereo setup included a double-DIN CD/Tape/FM/AM headunit, a tweeter in both door sails, one midrange speaker in the lower front part of each door, one smaller rear fill speaker behind the seats in the side body panel, and a subwoofer behind the drivers seat. A second subwoofer was added behind the passenger’s seat in 1993.
The CD player is fairly robust, although it tends to skip with time. The CD player can be fixed to correct this problem, although many owners upgrade to an aftermarket stereo headunit.