What setup are you using?
I don't have the higher end equipment that you have for them, but the NT-6 Pro capabilities scale very nicely for me with better source and a better amp. They are really power hungry, so adding my BH2 to the mix adds that bass thump as well as slam throughout the frequency range you mentioned you may be missing. I am guessing that the NT6 pro has even more to give with a better amp as well. Remember, this is coming from a guy that has not heard the NT6 Pro with your RWAK120 or Balanced 901 or paired them with your ALO RX MK3-B or your Apex Glacier. In addition, I have never heard your JH Audio JH13Pro, UE PRM, or your FitEar MH335DW to compare the with the NT6 Pro. I would really love to have some prospective of how these sources and amps pair with the NT6 Pro and how they come to your other CIEMs.
As for my sources, they really make my Clip+ sound incredible, but moving up to my C3/BH2 combo, it is a whole different world. The slam here is enough that they can become fatiguing during a longer listening session. Previously, my favorite pairing was the C3/BH2 believing that the DX50 and NT6 Pro wasn't a particular good pairing. Then came DX50 firmware v1.2.5 which changed everything.
Now with the DX50 using the new firmware v1.2.5, the sound is another large step up. I cannot listen to anything else without missing that sound. The new DX50 firmware adds a 3D aspect to the sound that the NT6 Pro responds to impressively providing a renewed sound stage. Plus the added warmth of the new firmware eliminates the fatiguing aspect while providing impressive slam even without the additional amp. The upgrade provides additional texturing, detail, and thickness for a more intimate, natural, lifelike sound. Another side effect of the new DX50 firmware is that the volume/power has somehow increased making the addition of an external amp less important. The addition of my BH2 amp still provides more realism/thickness/power in the bass/sub-bass response, but it is not as obvious as before.
VisceriousZERO, can you talk a little about how the NT6 Pro responds to your different sources and amps and how it compares to your other CIEMs providing some order of personal preference? Sorry, I know that I am asking a lot.