I trust you know that David at JansZen Audio continues to make repairs on the Nines (his father's design) if ever needed.
Also, he might provide a list of recommended amps.
KLH model nine full range speakers
Right now Iam using Plinius sa 100 amp. Iam happy with the sound and musicality. I just happen to read that Art audio concerto mark 2 can use KT 90 and KT 120 .I own this amp 40 watt per channel. Iam using 6550 tube the power it’s a bit short .. My two options to get KT 90 or 120. Or audition anticable autoformer to increase the power to 60 watts. Any comments thanks.