Separate subs for bass management & LFE in a surround set up

Everything Eric said.

I guess I should elaborate

The room is a custom design (golden ratio)
Floated floor, bass traps
Tons of absorption & diffusion on the walls & ceiling

All Martin Logan speakers & subs so well integrated
And the Trinnov preamp/processor to tune all the channels to match room response for amplitude, phase & delay

But since I've gone that far, I'm just trying to take any last possibilities into play. Companies that record for surround like 2L & Sono Luminus and definitely Steven Wilson purposely put a full range of sound into each speaker on the left side & right side of the array.

My question is more, will I lose some of the utility of the 1/4 placement for wave cancellation if both left and right front subs aren't playing the exact same signal i.e. left sub has left side low pass info and right sub has right side. If they both have the summed to mono total of all speakers then they will be playing the exact same signal, hence the bonus of cancelling axial modes. If they don't then I may lose that help in taming the room for a potential bonus of a moderately perceptible (if at all) ability to recreate the effect of using all full range speakers and the same imaging as the recording engineer's mix or better, the ambience of the room where a live recording was made.

My question is more, will I lose some of the utility of the 1/4 placement for wave cancellation if both left and right front subs aren’t playing the exact same signal

Yes.

Is it worth $5? Probably not.

What I mean is from an absolute testing / measurement perspective would you be able to measure a difference? Yes.
Would you hear it with real music? No.

E

Again I agree with Eric.

As you must be noticing multi-channel music post production is quite interpretive yet still manages to convey space for the most part. I'm guessing your extra low frequency concerns are more a matter of your rooms reaction to ELF and your personal taste.

I've set up my two channel system in three different homes, including one with similar dimensions as yours. Running my TWO subs in plane with the main speakers in stereo was only slightly worse than in mono and was confirmed by my subs built in Room Optimization software.

While four subs would completely change my situation I think I'd still be pessimistic regarding ELF stereo imaging unless you run two at unusually high crossover points. With the added flexibility of using four subs experimentation should provide you with far more knowledge and hopefully the results you're seeking. 

Not really what you are talking about but here is another way hook up your subs. 

JL audio subs will let you play both the LFE from your reciever AND the two channel high pass at the same time but you need a sub for each channel. 

JL audio inputs are summed. 

There is a right and left input on each sub. On the right if you send your right preout channel signal to the sub and from the sub to the amp. On the extra “left input” send the LFE channel. Do the same on the left side. 

This setup allows the subs to be blended with the mains through the crossover but still play the LFE signal. You can then boost the LEF from the reciver like normal and extend the range of your mains at the same time. 

I have ran mine this way for years with my subs set up for two channel but when using the HT reciver (by pass mode) the subs still play the LFE. 

For what it is worth I think subs can be localized (in a large proper room) and should sit beside the speaker they are extending.