Do No Harm ... well the least harm anyway

Hello koestner!  DBX makes a 2 way stereo/3 way mono electronic crossover (DBX223, be sure get the model with the kind of connectors/in & out plugs you prefer) and is transparent and reasonably priced. I use then in two of my 5 systems. They are a tweaker's delight, 24 db/octave and let you fiddle to your heart's delight. I agree that keeping the very low bass out of your main speakers is a good idea. I'm using Magnepan LRS and LRS+ in the systems with the DBX Xovers. My other systems use miniDSP electronic crossovers. Give each driver it's own amp. These days, good amps are not expensive. Happy listening.

Bomer:

I had the DBX Venue 360 in the system, but found it to be annoying having to run it through my computer. It was supposed to run on an iPad also, but they never fixed the problem that arose when Apple changed their OS a while back. I also did not like the additional A-D and D-A that had to be incorporated. I have been considering the Mini DSP Studio, or the Marchand passive crossover, but after a bunch or reading it seems this whole idea is a can of worms that I would probably have wished I never opened.

Hello, It looks like your subs have a 100 hertz high pass filter. Just run your line to the input on the DD15’s and then out to your amp. You might have to look at a manual but there is a 90 or 100 crossover switch on the back. You can at least use this to see if you like the sound or if it degrades the sound in any way. 

It looks like there is a thru output so you can do a little A=100hz or B=thru= 20 hz. 

please make sure you turn your equipment off before you connect/ disconnect cables. 

If those speakers have “Thumpy” bass it’s either your room or most likely the position of the speakers.  Probably they’re too close to the front and side walls.  
Before you try surgery or software, I’d start with pulling them three feet from the front wall.  That’s three feet from the back of speakers.

All the best.