Most people who are.. let's say more serious into this hobby simple defeat the rear speakers. Why? The art of getting a great SQ inside the car is
controlling the car environment - you control how these sound waves interact with one another. Controlling 4 drivers (2-way) or 6 individual drivers (3-way) is hard enough. If you throw in rear speakers, it simply shoots up the difficulty a lot more.
In the Philippines, I haven't heard a stereo system with a
properly implemented rear-fill. The type of rear-fill that adds to the ambiance or to your test sheet scores and not wreck the entire sound presentation. It says a lot about how hard it is in tuning one. If you plan on this route, going 5.1 might be a better idea.