for starters here is my setup. I have dual 12" rockford fosgate subs with a Rockford Fosgate R500-1 amp, i also just put in some Rockford Fosgate Punch P1683 in the rear deck speaker area of my car, i have a little bit of a concern with my audio situation, my speakers have no midbass! I have just recently put these 6x8's in my car so i dont know if there is a break in period and they will get more bass. I also do not have my speakers hooked up to a separate amplifier witch may be a problem with getting the bass. my sub amp's low pass crossover maxes out at 130 herts so that is why this is such a big problem. is there anything i can do about my midbass, or do i have to get different speakers (either different sub amp that reaches higher or different door speakers that hit lower) I have already checked and i do not have any crossover coming from my stereo that would cause this problem.
Prolly would try to add an amp to power your interior speakers. Make sure they have a high pass as well.
Common problem when adding subs. There is just not enough cone area in the speakers in the car to keep up with the subs. You did a good thing trying the crossover on the sub amp. Raising it to help the interior speakers is a great starting point.
Temporarily turn off your subs and listen to your 6x8s alone, If moving the balance to either the left or right results in more bass, then they are out of phase. If they just sound anemic and underpowered, that may indeed be the issue, just that they are not getting enough power. what kind of deck power are you running to them? Facory deck or aftermarket? Are they mounted in doors, dash, or back of the your car? Mounted to plastic, metal, or wood? There are lots of factors that will affect the amount of bass you will hear from a speaker, some testing will help to determine if it is power, wiring, mounting, or just a poor speaker.