Basically get your pld down to under 10Ē (.83ms) or abouts is ideal

Otherwise , for two seat tune takes some trickery and some settling on some big compromises on the center being solid and that is directly related to how low you PLD numbers are.

1. Use a 2nd order all pass with a Q between 1 and 1.4 centered between 200-300 (depending how wide your car is and those PLDs

Listen on both sides with no EQ applied against left and right. Whatever EQ you have make sure itís the same for both sides together

Get the center for both sides to sound as much as possible with that all pass

(It wonít be awesome but will be better than it was)

2. Carefully use EQ and gain and jump back and forth on each side and listen.

You want to listen for the frequencies that promote the center / left / right using a relative polarity track.

3. Use asymmetric crossovers if it helps get things working better. The time shift on the crossover can be used as your advantage to help move things a little.

Work on all of the above from 250hz to 1.3khz

4. Using eq shape the amplitude above 1.3khz to promote stage.

5. Use delay and polarity flips in all kinds of crazy ways. Make small changes. Stay within the limitations of the frequency dependence of that passband. (You have to convert milliseconds to feet and to frequency......) a mid to midrange with a crossover of 300hz could be as much as 1.6ms difference from actual distance.

6. Do all of this in no specific order. Itís a matter of making good judgment on what needs what as you listen.

7. If PLD is under .5ms good chance the AllPass wonít be needed at all.

8. Make whichever pair of speakers that has the least PLD be the first to arrive
By using delay (use the hass effect to your advantage) this is not a necessary step but can help quite a bit on lower midrange.

This is the Non-FIR approach that works decently.
You should get both sides to have

a. Non biased sides
b. Spectral balance on both sides

You probably wonít have a super solid center , it will be very diffuse and probably be midbass heavy (200-450hz) and the flatness if desired response may be unachievable if you PLD is too large. If you can get your PLD under .5ms the stage can be easier and easier and better and better the closer you get to no PLDs. If you PLD is under .5ms you can have just a good a stage as a one seat tune in every fashion and in my opinion itís better than using a bunch of delay on one side.