You have the amp idea right, but the tweeters and woofers cant come straight off the headunit

(unless you have a very expensive one with an active crossover) as the different speakers can only play certain frequencies and if you try to play the wrong ones through them they will distort and cook the voice coils, we use capacitors to stop the wrong frequencies getting to the speakers and they can be on boards called crossovers, the only drawback is the caps use power hence we always recommend you use an amplifier to run component speakers not a headunit.

The mr2 as standard has a full range

(can play most frequencies) speaker in the door and a tune up tweeter

(which has a capacitor on it to block all but the high frequencies getting to it).

You will probably be getting a set of component speakers which will come with the crossovers which has two inputs

+ and

- for one twin core speaker wire and two outputs

(can be 3 or 4 for 3way set ups etc) one for the woofer and one for the tweeter, and it is important the speakers are fitted well with a seal all the way round so the sound from the back cant get to the front as it will cancel each other out, it is best to use mdf adaptor rings.

HTH