To tweet or not...

Thanks Bob!  I will look into the Townshends.   

Hi mechans - yes, the MLs are electrostatic.  Why would that make a difference?  Thanks! 

I doubt it !  Aren't ML electrostatics or are these boxed ?

I, too, have been intrigued by the super tweeter addition. I know Townshend Audio makes one. If I were to do it, I would contact the manufacturer and give them all the details to see if it will work before buying.
Kalali's post has me thinking this addition may not be as easy as they purport. And, I know he has a lot of experience with building speakers.

Bob

I can’t comment on your specific system but adding a super tweeter is not as simple as you might think. To do it right, you will need to make sure the super tweeter has similar or very close sensitivity; dB/1m/1w, so the volume matches the panel’s output. You may also need to build a simple crossover network so the frequencies don’t interfere. I tried adding a super tweeter to my single driver full range back-horn loaded speakers but I had hell of a time finding the right brand/model and getting them to blend well.
I hope more experienced speaker builders will chime in with better guidance.