On a journey for the last couple of years

The 761is a stereo amp with dual mono construction.  rather than purchase two - if you believe you need that much power - for $14k a piece, I’d buy one 861 for $22k and call it a day. I have a good friend who has the 861s with Wilson Sasha Vs and he loves it.

@peterrock Great plan... Many times, in this hobby figuring what next move will provide the biggest benefit is somewhat a guess.  In your case, however, as you can see from the majority of recommendations the direction is pretty clear.  The good thing with your approach is that even at some point if you move up several levels in amplification quality subs will still be a major benefit.  All part of progressively building a better and better system.  

With respect to hiring a professional, as you’re already requesting, getting recommendations is really important to be sure you get the value.  I would also offer that there are some free services, like with GIK Acoustics, that will help you analyze your room and provide recommendations for treatments.  Certainly something you can easily do in stages and typically very simple install.  Typically like hanging pictures.  It’s amazing how much difference some simple treatments can make.  With respect to subs, REL also has a lot of info/videos on-line as well as real people to speak with to walk you through placement and tuning.  This can be a little time consuming but again is not rocket science and can actually be a fun part of learning. 

Best of luck...

yes, it's a good idea to have someone look at your system. You could look for a local audio club, or if you can pay for it, hifi stores offer this service for a fee. 

Unfortunately, the 2nd option is often futile, employees at hifi stores just want to sell

@peterrock Lots of places that sell room treatments have free help. They will guide you on finding the first reflection point. You give your room measurements and they work out a plan with you. It’s not difficult. 

@OP Regarding some early comments about frequency response. Low E on a four string bass is 40Hz. Low B on a 5 string is 30Hz. So unless organs or electronic music is involved, in a real room, extension to the low thirties is plenty. When we are focusing on bass punch in mixing, we're looking at 200Hz 500Hz.

I suspect what you are looking for is more slam. I think your speakers are fine as far as bass punch goes. Slam is more about transient response, plus the capacity to move air. Amplification and cables are certainly worth looking at.  I would add Dan Dagostino to your list - an audition of the SIM Audios or a pair of Progression 550s will tell you what you need to know. If you are looking at an upgrade speaker wise, a pair of Wilson Sashas is worth considering and also possibly also the new JBL Summit series. I've only heard the two way Ama and it's very impressive scale and base extension-wise for a compact two way so the Makalau should be even better.