There is a direction that you might consider, I am taking about lower bass channel. I know that you have your wet dream fantasy about large midbass horn but there is topological restriction for you: time alignment. I do not know how to address this problem. The itch for midbass channel is not juts chowing over the “never stop paranoia”. The type of the drivers you use at LF are very good in my view at bottom but above let say 60-70Hz your can do better. You bass drivers have unique non-inertia rubber suspension which doe not feel like rubber and sonically very far from typical rubber used but it still not as loos as vintage paper suspension or leather suspension. Playing some lower MF or midbass instruments, you might feel that the micro-tensions and transients in midbass will be slightly mad out with your bass drivers. Honestly, it will not be felt as “deficiency” as those ScanSpeaks are very nicely balanced. What I did at my time was experimenting with loading. For instance, if I drive your bass driver from 6C33C then the best sound at 40Hz I got when I was loading my amp with let say 400R. However, the best sound at 120Hz I was getting from the same drivers if I load the amps with 1200R. At 1200R ScanSpeaks “ring” like a good vintage driver, well sort of… The irony is that in your configuration it is even possible to do it driving different section of the drivers in array from different taps of your OPT or even from different channels or Milq. It because a bit complex and you need to deal with power matching and a few other factors. I do think that much easy way to introduce little ridicules dedicated midbass channel with nice “loose” vintage driver, similar to what I did in my current room. The “ridicules” part come from that fact that it is not proper speaker. Above 125-150Hz you will have your upper-bass horn take over and at sub 70Hz you have your line-array cover nicely. So, it needs to be a very small little direct radiator box with 100dB efficiency. All that you need this driver to do is juts to inject some textural ringing around 100Hz. The wonderful irony is that 70Hz-100Hz is the exact location where most likely your room modes will be showing. So, you can combine your “injected textural ringing” with amplitude correction – very slick and effective way to deal with problems.