Does anyone here have any experience in regards to replacing the Sovtek 6922 tubes in an NTK with a "better sounding" type?

I Bought an NTK some time ago(all the hype got me), but I've since been rebuilding my room, so I haven't had an opportunity to check it out yet. I understand, like everything else, mics are subjective...heard good and bad about the NTK. However, when I hear things like, "sibilance problems", or "thin sounding," well, that concerns me.

I was looking for a review about the new K2...curious about how it compared to the NTK. Didn't find a review, just some opinions in a different audio forum. But I did come across a post in that forum that mentioned the Sovtek 6922 tubes in the NTK were far from ideal, and suggested that replacing them with vintage tubes, or something like Siemens, Svetlana, or Electro-Harmonix, would make the NTK much more usable...fuller and warmer were mentioned.

Does anyone have any experience with this...or advice?

Thanks --Brian