When I had my Octave V70SE then later the V110 I had used the RCA triple mica black plate in place of the 12ax7 input with great results. It was a warmer overall sound. Of course I did get the OK from Andreas Hoffman at Octave. He also said for those integrated amps 12au7 could be used in place of the 12at7 driver/splitter tubes which is also a lower gain.
That said I would contact the manufacturer and ask if changes like those will work. Some manufacturers design allow for flexibility while other do not.
That said I would contact the manufacturer and ask if changes like those will work. Some manufacturers design allow for flexibility while other do not.