I have always installed my component/coaxial speakers with a high pass crossover set at about 80HZ, letting the subwoofer supply all of the low end. Recently I did an install for someone who questioned the sound that my install yielded. So I shut the crossover off and let the front speakers play full range. And it sounded A LOT better. Fuller.
Here's my problem. The front speakers in my next install are a 3 way component set from MB Quart with their competition passive crossovers. I have one 4 channel amp and one 2 channel amp. I will have the 3 way component set up front, a coaxial pair in the rear, and a trio of JL 10w6's in the trunk. The 2 channel amp is for the JLs. The 4 channel should be for the component set and the rear deck coaxials.
To get the "fuller" sound that I liked in my last install I will need to leave the 6 1/2" midbass driver unconnected to the crossover, right?. Using my current equipment, how do I wire the front 6 1/2" drivers separate from the speakers on the crossover AND keep my rear deck speakers in the loop.
I say spend $200 and get a Phoenix Gold active crossover to put before the amp. It'll let you tweak and vary the cutoffs quite a bit (even stereo vs. mono) to get a good balance. The passive crossovers should be left as-is, since they're also preserving the powered range sent to each of the components.
You generally don't want the highs coming from the rear, because it throws the sound stage to the middle of the car (instead of the windshield, where it should be). You would, however, do this if you wanted full sound for rear passengers.
Check those components and see if they've specified for "on-axis" or "off-axis" placement, too. Anything on-axis should be door or pillar mounted, while off-axis should be deck/dash mounted. Axis is relative to the side of your head (i.e., ear). Poor placement can really change the sound of good components.