$16K new/used speaker question?

After reading the comments from your original post, a brand that has not been mentioned and that I have had complete success with are Usher BE 10's. I have had numerous Wilson products starting with the 3/2 up to the 8's and has out performed them in every way. I have a pair of Carrie 211 FE if I'm not mistaken are close to the wattage output of your gear. They are rated at 91 DB and 8 ohm load with no huge impedance swings. I suggest taking a serious look at them and note their driver selection.
Happy listening,,,!

Hi Tom, you are definitely on the right track to meet your goals. I previously owned the Devore 9 (5 years) and now own the O/96 and they are very responsive to quality tube amplifcation. I got a chance to audition the 0/96 and the Gibbon X side by side, and I actually preferred the 0/96, but I think it would come down to personal tastes. Both are full range (at least enough for me), coherent and have that hard-to-describe sense of "humanity" to their presentation. The Devore 9 is not full range, but the 0/96 and the X both have terrific slam, depth and definition in the bottom octaves. Now, I have not heard Acoustic Zen speakers but I have always wanted to, and I suspect the Crescendo would also be a great choice. I have not heard the Daedalus line either, but they have many fans among tube users. I have owned at least 20 different brands of speakers through the years and until the Devores, my favorites were ProAc and Verity. I am convinced that for a tube lover, speaker choice should be guided as much by the speaker's impedance characteristics as much as anything, and the Devore speakers are ideal in this regard. Best of luck, I don't think you can go wrong with either of your top choices.

Why 8Ohm/90dB+ requirement ?

 VK-150se monos can drive almost any speaker. You are missing out a lot of great speakers.

Tom, I have enjoyed your posts over the years and happily weigh in here because I just went through a year of searching for speakers in the $15k used bracket.  I listened to a lot of different brands.  I too was looking for greater bass depth but unlike you, I have a 300 wpc solid state amp.  First off, I think you should not be restricting yourself to high efficiency designs because your BAT's will power just about anything unless you listen at abnormally high levels.  

I rejected the Acoustic Zens (too boxy sounding), Vandersteen 5A's (not as detailed as I want--but I liked the 5A Carbon above my price range); I think the Wilson Sasha 1 are a good buy at 11-12k and provide superb mid bass dynamics; but I really like the Magico S5 --at about $15k-- wonderful extension on both ends, maybe the best bass I have heard,  and judging from the Myles Astor review will work with tubes.  In the end though I purchased a demo set of TAD Evolution Ones-- I really like the concentric design which seems to make the speakers disappear. Plus they are very dynamic and detailed. The beryllium tweeter is very well integrated as on the S5.

You have gotten it right with your current amp speaker matching--a tube amp with a metal tweeter is a great combo.  The YG's are a very advanced and coherent speaker. Replacing them with speakers of lesser coherence and quality to get more bass is in my view a mistake.  So if I were you I would definitely check out the Magico S5 or the TAD E-1.