Which would be better? 6X9's in the bottom of the door,or two 8" subs under the seat? These doors are metal. The radio is pushing somewhare around 50 watts max out all 4. I currently have 2 3.5's In the upper portion of the door.
Thanks.

 

2 8"s under the seat would be much better if what your looking for is to add bass. 6x9s would work, but than you will have to deal with noise from the door.

 

Dupuis is correct. It depends on what you are wanting from the set-up. 6x9s are NOT good for bass. The best 6x9s on the market are very average in terms of sound quality, and are in no way meant to be anything more than midbass speakers. That is why there are dedicated subwoofers. With the 3.5s, your system is very "light" in the midbass or midrange area. So 6x9s would help in that regard, but not for true bass. And if your head unit is "marketed" as 50watts x4, it is more like 12-15 watts at its best without distorting terribly. If you were to drive it to produce anywhere near 50 watts, it would sound horrible. That's just the way HU amps are. They are not well suited for anything but low to mid volume listening. They are very limited in terms of power supply capabilities. That's why there are dedicated amplifiers. However, that's not to say that someone can't be happy with a system without amps and subs. It's a matter of needs and wants and tastes. We're all different.