I already have Bose and Harmon Kardon systems in my other two cars, and putting the amp and speakers in my truck isn't worth it, so I'm selling the stereo from my STi. It still have all the wiring attached and will be an easy plug and play in any WRX or STi. The specs are:

4 channel Alpine amp
2 x 6 1/2" Alpine R series component speakers - the best Alpine makes, the magnets weigh about 5 pounds each!

I also have a set of Kenwood component speakers that I can sell with it. They're 5 1/2" speakers that were in the rear doors.

Take it all for $300 (plus shipping). The speakers alone were more than that new, and so was the amp. They also come with big gold cables to connect the amp to the head unit which were $40 I think. The sound quality of this system is about as good as you'll find.