As displayname suggests above, the MastersounD Dueventi is a great product for the JBL. I have 4311 here and the previous owner was also using a Dueventi to run them. I’ve done the same here and it is a marvelous pairing.
The Dueventi pairs well with the tweeter and also is a smoother presentation, which eliminated some of the bloat that the JBL have in the bass.
Another 'pro' for the Dueventi is the stock voicing. Somehow they got it right with the stock JJ 12au7 and EH el34 tubes. This means when the time comes to retube, you can do the entire amp for right around $100. I've had clients try to roll in NOS tubes and they've reported back very challenging work to best the stock configuration.
