Three tube preamplifiers were used with ATC 40A and ATC 50A transducers: Manley Jumbo Shrimp, Manley Neo Classic 300B and De Havilland Mercury (heavily modified) were used for years in my system. Each time I felt the tube design could not keep up with the speed of active speakers. There was a smearing I could not resolve.
First switched out to Sugden LA-4 class A. That gave the speed needed. Then to Luxman C900u preamp for the complete sound. Your mileage may vary. Best success. Cheers