I think you're in for a treat my friend!
Re: the RCA 14F7 which I got today, it is another wonderful tube, so it goes into my top 3: TS5751, TS14AF7 and now RCA14F7.
I had a moment on another planet agin when I first tried it.... to do with the ambient music I had on as well as the tube, so to try to retain objectivity I went through my test tracks again. I expected it to have a nice musical balance being an RCA, but I didn't expect it to have great detail and soundstage, like the other 2 tubes. On that first piece of music I tried, the soundstage was wide, deep, and all enveloping, but this depends on the music and I think that the other 2 tubes are fairly similar. It gets more and more difficult to separate the small details between tubes when they are at this top level. As a 14F7 rather than a 14AF7 it has more gain as expected which makes it better for me but I didn't find it any more forward or harsh which I suspect is more down to the type of 14F7. Once again the realism is there, also I found it going down to really deep bass which is something that I hadn't noticed before, I may have just missed that before, but the bass was more of the type you feel rather than hear, it was that deep, and that makes the music very full sounding. The thing that made it difficult was knowing the construction was pretty identical to the TS14AF7, I didn't know if the RCA was really a Tungsol in disguise lol.
So to sum up:
1 - TS5751, treble has a silky sheen to it, very liquid, but still has the dynamics when needed, detailed, controlled, open soundstage
2 - TS14AF7, still smooth, more neutral and extended treble, more live sounding, detailed, open soundstage
3 - RCA12F7, this was the surprise. Smooth, detailed, fairly neutral, live sounding, open soundstage, I found it enveloping but mainly down to the music being played, extended bass.
I would rate them equal, but my preference is for the TS5751, followed by the TS14AF7, then the RCA14F7, but they were all very close.
Looking forward to your impressions of the TS14F7 Maxx!