@james633 --
Congrats on your JBL 4367’s. I find them to be an impressive design from a relatively compact size factor, and agree that stands should be included. There’s something about the good old "15 inch woofer/mid and a horn" combo that has a timeless appeal as a very versatile, coherent and powerful sounding system. Perhaps a core element of this is the crossover region of these designs typically placed somewhere between 500-800Hz, and what it offers with a point source above in a large frequency span as well as an untarnished "power region" (say, 150-400Hz) below via a large coned driver where no crossover point is placed. Having a large radiation area here lends a fullness and vitality to this region that smaller woofers and midrange drivers (and often in multi-way designs with a XO point in the power region) simply cannot replicate.
I agree with poster @mijostyn’s good advice on high-passing your JBL’s for subs augmentation, though do it right - i.e.: also be mindful of the type of subs chosen, but as an outset you have a pair of JL Audio subs to experiment with, so see what you can harness it all into, and whether it coheres fittingly into a whole. Ultimately I’d go higher efficiency sub designs like the ones meant to be paired with the M2’s, as I suspect they’ll blend more seamlessly with type of woofer used in your 4367’s. This is not trivial, as I have tried out different constellations of higher eff. mains with lower eff. subs, and personally I find they just don’t mesh properly - for a variety of reasons.
As it is they’re still very capable used full-range (the only way I’ve heard them), and given their moderately high sensitivity and large air radiation area the doppler phase shift phenomena mayn’t be as pronounced here. Certainly using dual high eff. 15" woofers up to ~600Hz per channel in the main speakers (like I do), full-range, they have to be spanked pretty hard for the cones to move visibly, and when high-passed at ~85Hz to high eff. subs there’s zilch movement even at war volume levels.