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.
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.