I can't tell you what happened to change things from the way they were at one time. but I have been convinced since fairly early in your thread that the problem was in the mid-bass range, which is typically thought to start at about 50Hz. Low acoustic instrument sounds, like the fundamental notes of a kick drum, only go down to ~ 50Hz. Some electronic music, and harp, piano, and organ music, can obviously go lower than that. But, the majority of the bass that we notice most in music is from about 50Hz and up.
Depending on a number of factors, including placement, subs may not deliver as much mid-bass as we like. If our main speakers don't do their part, we may have to explore ways to better integrate our main speakers (via experimenting with different crossovers, since we can rarely change their placement), changing to more capable speakers, or adding a mid-bass module to augment the mid-bass.
At this point, you may not ever know exactly why you are not getting the mid-bass you want in your main system. But, I always thought you should focus on experimenting more with the fronts to find solutions--some method of operation that seemed to improve the sound. If you are replacing your front three speakers with more powerful ones, that should help, and you can certainly wait until they are installed to do any further problem solving.
If, however, you want to experiment now, I can't think of anything else to try except adjusting your crossovers (up to about 120Hz and down to about 60Hz). I can tell you emphatically that where main speakers are capable enough, they can contribute significantly to the mid-bass. Audio experts (and sub makers) such as Mark Seaton and Jeff Permanian (JTR), among others, strongly believe in the importance of capable speakers to support the mid-bass from 50 or 60Hz up, even with some of the best subwoofers in the world, and as a result, they design speakers with that capability. Many other makers do, as well.
So, I think that the long-term solution is going to be more capable speakers, and/or a mid-bass module. Typically, a MBM, such as the one described and tested in the following thread, has a HPF of about 60Hz in order to give good mid-bass support and increased tactile response. https://www.avsforum.com/forum/113-su...-response.html
Short-term, you can certainly experiment with ways to improve your mid-bass performance via crossover changes (it takes about 10 seconds) but I doubt that you will get all that you are hoping for until you change to more powerful speakers, or perhaps add bass traps, or rearrange speaker locations, etc. Hopefully, better fronts will solve the problem.