Importance of phase and timing optimization when incorporating sub woofers ?

Yes Duke but FR, Phase and Time interact. In order to get the frequency response right it helps to get the timing right. I have continuous control over the delays of each speaker and subwoofer and can make adjustments by remote. I can hear exactly what happens. When I run an impulse test on the system the computer will automatically set the delays so that the sound from each speaker hits the listening position at exactly the same time in phase. It also calculates filters to make the frequency response dead flat over the entire spectrum. I can overlay target curves on top to give the system the frequency response I like. Also remember like you I use 4 subwoofers. If I bypass the system it is a very dramatic difference. The image blurs, the bass gets funky and there is too much treble. With the system on you can't tell there are subwoofers until a real low note comes along and I cross up high at 125 Hz. 
Jim, having phase controls on subwoofers is not quite a gimmick but close unless you have a method of measuring delays and frequency response. Doing this by ear is next to impossible. Having room control in the sub is a dual edged sword. It does not excuse you from doing proper acoustic management. The bass will only sound right where you place the microphone and off everywhere else. If there is a 6 db null point at say 40 Hz at the listening position your sub's amp will be forced to put out 4 times the power there. If there is a 6 dB peak 8 feet away that peak now becomes 12 dB. The best way to deal with this is by having multiple subs. I find it interesting that both Audiokinesis and I both landed on 4 subs. It is a more effective way of dealing with room acoustics especially if you do not have measuring equipment. 

The Rythmik Audio subs that contain one of the company's "Full" size plate amps (A370, H600, etc.) have a continuously-variable phase control, allowing adjustment anywhere from 0 to 180 degrees (no delay to 16 ms). And if you choose Rythmik's OB/Dipole Sub, it will excite fewer room modes than will ANY single omnipole sub.

Having the luxury of visiting many show rooms in Las Vegas, I learned that sound engineers utilize near-field subwoofer placement to solve a lot of bass problems. Specific show room pending, I’ve seen individual subwoofers serving no more than 12 seats per array. How they solve group delay and echo slab in a 2,000 seat room is another matter and them sound-techs weren’t to quick to divulge.
The advantages of using multiple subwoofers had been promoted to death. Off to the opposite extreme and for the normal one to two center seated listener, I’m an advocate of placing a subwoofer right behind the main seat. With main speakers capable of good 40-50hz extension, the sub can be crossed low enough to avoid any directional clue (provided with low distortion high quality sub and 4th or higher order lowpass)

Advantages:
1. Minimum sq.ft. displacement. (One sub and no clutter)
2. Minimize room node problems for one position.
3. At typical distance of main speaker of 12-15’, phase difference with sub is nominal at these frequencies and easily compensated.
4. Due to close proximity of sub, high power isn’t necessary.
5. Equalizing mainly to extend or smooth sub’s natural respond due to minimum room influence at listening chair.

To address time alignment, I’d learned a trick from videophiles by using digital delay they use to lip sync video/audio. Bit perfect not withstanding, one can delay digital signals going into either the main or subwoofers in 1ms or less increment. (1ms approximates 1.36inches) Yes I’d tried driving the main and sub with a pair identical DACs experimenting with various phase and time alignments. And believe me that it is nearly impossible to identify arrival peaks of the sub using impulse measurements. Main speaker will show distinct first arrival peaks/dips but subwoofers are nothing but a smooth gentle wave that looks almost like a straight line. Best compromise is to physically measure the distance and compensate arrival time.

No I don’t hear much of a difference with sub time alignment but phase i can. It is easier and more impactful to compensate for phase. Oh... sorry I got side track...

Best Regards

audiokinesis2,  Wow! Your post above was a gold mine of information..

Mijostyn wrote: " Yes Duke but FR, Phase and Time interact."

Agreed! Of course they do.

And I bet that when you get the phase and time right, the frequency response is also right. 

Duke