I used to own a pair of Marantz EL34 mono block amplifiers that used one each of the E88CC/6922 types. Back in 1986 I had bought 10,000 NOS audio tubes from an estate and this guy must have used this type of tube as there was a lot of them.
99% of what I tried sounded nice, but the top of what I had, that were NOS were the Valvo CCA and the Telefunken E88CC. I have a couple sleeves of RCA branded "Made In Germany" tubes (not Telefunken) that sound outstanding as well. I never looked into what brand they are but they are West German, maybe Siemens or Lorentz. The Amperex 6922 "PQ" tubes were very nice as well and I'm sure I'd have a different opinion in different amplifiers. I sold the amplifiers many years ago but still have many of the tubes.