I want to find some 70 watt RMS 6x9 coaxial speakers. I am not looking to get a subwoofer, so I mostly am looking for the speakers with the greatest frequency response range. I know that's pretty hard, but can you just tell me some brands that usually have good bass?
You could get some Tang Band 6x9 Woofers if you really want bass in the rear without a "real" sub. Then run some nice hi's in the front you are set. The Tang Bands are just woofers.. no tweeters.. but they are going to produce the most bass for a 6x9 speaker.
or you could get the ones i quoted from parts express.. wire them together for a 4 ohm load and bridge 2 channels to them.