Best place to put a single subwoofer?

Martinmobile, imo/ime, all seems in order, except for two things. Because of the omni pattern of the MBLs, much is being absorbed by your panels, although I do tend to like a "dead" wall behind the speakers. As an experiment, try removing some to see if the slam comes back, even though the brightness will return. Second, the level of your equipment deserves a second sub. Room coupling is always better balanced with a pair, ime. However, as I stated, getting the "right" subs to match the mains (coherence, speed, tone, etc.)is a bitch, and much harder as the system gets more "refined". This is why many people (Audiogon type) do not like subs. Much of the "slam" you are looking for is above the subs crossover point, so it might not be the sub issue. Are you running the MBLs full range, or rolling them off at the last octave ?(again, very tricky if you are). I am not one to think the BAT gear to be the most "ballsy", ime, but your amps are great none the less. Are your tubes (pre amp) experiencing microphonics ? I would love to listen to your system, as I am huge MBL fan (although I own horns, which is another thread altogether). Keep us posted. MrD

Hello Everybody. Hello MrD, Thanks for the feedback. I am not rolling off the last octave and I am in fact running the MBL's full range. I am not a big fan of routing the audio signal through Hi-pass filters in the subs crossover. I have found that to degrade the sound to the main speakers, in my experience, so I run my sub straight from my preamp, X'd-over at between 50 and 65hz. My MBL's run full range. (I did the same thing with the Martin Logans and the plethora of subs that I mated with them. Allways full range).
I agree about the running of stereo subs as I have indeed done that. Dual Velodynes, Dual Bagend Infrasub 18's, Dual Von Schweikerts, and even Dual Sunfire "True" Subwoofers-God forbid! (which by the way were absolute pieces of shit for music. I refer to them as "nuclear bombs in a small box"- No pitch definition, 1 note bass pieces of poop that they were!). Yes it is difficult to make a pair of stereo subs integrate properly, and does not take much to overdrive the hell out of the listening room.
I have given some thought to the fact that maybe I "over-damped" the wall with all those big panels I had made, and have considered taking a few of them down, like maybe 2 of them. Leave 3 up? But I have not done that yet. The one thing I am mindful of is how much that wall behind my MBL's reinforces the sound, making the overall musical presentation rather "bright" and "strident" sounding. Not a good thing IMHO. Been there, done that, didn't really like the effect. Room definately sounds better with a "dead" wall behind the speakers. But I should try taking a FEW of them down and see what the effect is. Good suggestion MrD.
As for the tubes in my preamp going "microphonic"?? I haven't a clue. How would I know? What is "microphonic" anyway? (showing my tube ignorance now. This B.A.T. preamp is the first AND only piece of tube gear that I've ever owned. Always had solid state my whole life.) I have heard the term "microphonic" used, but wouldn't know if something like it is occuring with my toys. Please enlighten me if you would?

Martinmobile, microphonics are the result of unwanted vibrations via acoustic (airborn) or mechanical feedback, usually re-amplified through the system. These can enter (or exist in) the preamp chassis and screw things up. IME tubes are more prone to this, although, it is everywhere and in everything. I believe heavily in "tube dampers", as I feel the sound is cleaner and tighter. BAT might have included them with the pre amp. They look like garden hose washers (as an example) and come in different shapes, sizes and colors. There are so many tweaks available to "tighten" up the sound. You are free to email me and I can discuss some of these with you. Taking panels off the speaker wall would be an experiment to see if " slam" is increased (brightness too, unfortunately). Let me know. MrD.

Martinmobile, anything new to report ?

Under the center channel! It will blend PERFECTLY!