One last suggestion.....
Go and borrow a Klark Teknik DN360 from you know who.
I know he won't be using it for a while. Then you can fiddle about to your hearts content looking for the culprit frequency/ies.
If that solves the problem, then maybe you should look at alternatives to just room placement and treatment.
If you can't get a hold of it, tell me, and I'll send you my Crown EQ2. I just know it will do the job.
Or, go and buy yourself a DBX PA thingie, and you can do it all in the digital domain, if you don't want to try analogue.
I know, you want the speakers to be able to do it themselves, but, there are too many variables.
Also, you're comparing the 1400's to the 4350's which you've become very accustomed to. BIG difference and absolutely no comparison.
What you may hear in one, you might not hear in the other and vice versa.
You're gonna end up chasing your own tail into oblivion, if you don't make sacrifices.
One shoe does not fit all! If you want the shoe to fit everything, invest in a GEQ.