Thanks for all the input, guys.
$10k is an arbitrary number. I like my Aperions, and honestly, when I bought them I figured they would be the last speakers I would ever buy, and cost way more than I ever thought I would spend on speakers. I think they sound great for music and movies. They fit the room, they work well with my components, my wife tolerates 4 of them in the room, along w/ the 2 big subs. All is peaceful, harmonious, done and done.
BUT, simply put, I got the bug and a little disposable cash in my discretionary fund. (We learned some time ago that single combined bank accounts and budget were a problem. I'm a spender. My wife is a saver. I handle the investments. She handles the budget. It works well, but I was frequently trying to convince her I needed X$ out of the budget for some toy. So we set up individual discretionary accounts, and we each get an allowance deposited into our accounts. We can each spend that money at our discretion without affecting the budget. I can save for a while, but then start to itch... and have to scratch.)
So now I'm thinking about scratching some speakers. These will be the last speakers I buy. Ever. Really.

The $10k range is just what I suppose is enough to get a significant improvement from the Aperions, and enough that the next significant improvement, (8Ts?), really is more than I will ever be willing to spend.
I still don't understand going the route of a separate music system. If I have premium l/rs for music, why not simply use them for tv/movies also? Maybe I upgrade the center, maybe not. I think 4x Aperions Grand Towers for l/r & rear surrounds is plenty for me.
There is a custom audio shop near me that is an RBH dealer. Don't know if they carry any stock or not. Need to call them. And need to investigate the other brands suggested here. Walter, yes, I looked at your system. I appreciate all the comments from members here. But in addition to someone's comments, it's interesting to see how they spent their own money.
Thanks again, guys. Have a lot of homework to do.
I think that about sums it up. I agree with you about not understanding music only systems. If you have a good set up then if you switch off the screen you have a music only system. This can be two channel or multichannel.
Personally I really like to have the picture with my music. To all intense and purposes I don't listen to opera anymore, I watch it. I really like my symphonic music with a picture now. It is much more involving and in many ways though different to being there is valid and in many ways better than being there. I doubt I would ever put a system together without a screen again.
I have been enjoying the Proms both with picture, three per week are broadcast with video, and the others audio only. This year I have loved it, as you can download them from iPlayer and then you never get buffering. Picture and sound this year have been totally amazing.
The HTPC I built a couple of years ago, has been one of the best things I ever did. I use it more than any other of my front ends.
As far as the center is concerned. That speaker is more problematic than any other. If you are going to listen and watch the sort of program I do, it is vital to get it right. The sound must be seamless across the stage. The center of the orchestra must be in the same acoustic space as the sides. As a singer moves across the stage, there must be absolutely no discernible change. Getting this right took more R & D then anything else to create this system. The center went though more iterations then anything else. I have not felt the need for any changes in about two years now, so I'm confident I have it right.
As you know I regard timbre matching as making sure all speakers are equally lousy.
One of the things in addition to frequency response is lobing. Getting this right is essential to a seamless sound stage.
My view is that having the left and right speakers MTM is a good start to success. An alternative is a coaxial approach, as long as you can get enough power handling.
MTM has a number of advantages for multichannel listening. Done properly dispersion is symmetrical about the vertical plane, and can be tightly controlled. Horizontal dispersion is excellent. It minimizes room problems, especially from ceiling and floor.
Creating a lobing error by turning an MTM on its side stands out like a sore thumb. At least it does to me and is never convincing.
Unless you have an acoustically transparent screen, then using an MTM vertically, gets the acoustic axis too far from the screen.
A coaxial driver or full range driver fits the bill best. The driver can be placed directly adjacent to the screen. Dispersion is conical, which not only blends well with an MTM dispersion pattern of the left and right speakers, but minimizes interference with the right and left speakers. A nice cone of dispersion should result covering the listening area. One is then left with the task of making sure all front three speakers have an excellent smooth frequency response. Since the drivers are different, this is easier said than done, but with patience achievable.
The other option for the center is a three way, the tweeter above the mid and side woofers operating below 350 to 400 Hz range. There will be a non symmetrical lobing error, and so it likely would be best to have the left and right with a tweeter, mid, woofer configuration in the vertical plane. I would think having the same order crossovers to match the lobing errors would be desirable.
As far as the surrounds and rear backs, these are high in the room especially the surrounds. The crossovers produce lobing errors with a tilt down to the listening area.
This is how DIY helps achieve what can not be done with commercial designs. DIY allows for a totally integrated approach.
As far as multichannel algorithms, I use two. I use Neural THX for live broadcasts from MPR encoded in that format.
I use Dolby Dolby PL 2x. My observations are that pop music mastered two channel sounds awful with this algorithm. LPs can only be played back two channel.
Most classical digital recordings benefit. In fact results are almost as good as with discrete multichannel recordings often. This has been particularly true of the BBC Prom broadcasts from the Royal Albert Hall. It is just uncanny how these broadcasts really sound like the RAH with Dolby PL 2x.
If it is a recording were Dolby PL is a detriment, then it is easy to revert to two channel stereo.
Since you seem ready to spend significant coin on a new speaker system, I have tried to answer your original question to the best of my ability.