I believe I had the Series IIs.The series Is were the best and the series VI were the worst. I owned both. I wasn't exposed to much hi-end audio when I bought my first pair in the early 70s. Now even Bose has given up on the 901s.
Still in use today by my ex brother in law!
For their time they were great.
Got them from the old man when he moved to Venezuela.
They were hanging from the ceiling in their den.
His main system had Dahlquist DQ10s with the passive subwoofer.