I just finished having the new stereo and radar installed in my '08 WRX.
Here's what I did:
Alpine PDX 5 under the driver's seat.
Pioneer DEH-P7900 BT Head unit
MB Quart RVF216's in the front doors with a complete dynomat job on the doors as well.
JL Audio 10w3v3 sub woofer in a simple box that sits in the hatchback area.
I also had them (Custom Audio Design in Silverthorne, Co.) install a Rocky Mtn Radar system that does a very good job of radar and laser detection.
All in all, this system rocks!! The alpine amp is unreal and the head unit with Bluetooth is great. The sub woofer is plenty for my tastes in music but might be a little light for the hardcore hiphop crowd. For the $$ this is the best sounding system I have ever had.
The only thing I have left to do is to dynamat the rear doors and replace the rear speakers. I am thinking of another pair of MB Quarts or possibly Alpine. I would love to hear any feedback on the new Alpine speakers.
Also, for the record, the WRX is definitely the way to go for commuting (daily) through the Eisenhower tunnel at 12,500 feet of elevation.
Love the car and I really love the stereo!!