Well, I must hand it to you tube lovers...your info has been spot on, they sure do add another dimension to the music. I recently picked up the Music Hall dac25.2 for the very reason of adding a tube into my system. It sounded very good with the stock Russian 6922 tube. But I knew that a different tube would definetely elevate it's performance.
After talking to Stephen at Quest for Sound I decided to give the NOS Amperex Bugle Boy (1958) tube a whirl. Stephen reminded me not to pass judgement till it had a good 100 hrs on it. He did however say that I would immediately hear a difference compared to the stock tube. He was dead on! Right off the bat the music was more detailed & a lushness was added that I didn't notice before.
I then let it run for the alloted 100 hrs (sneaking a listen hear & there) & it just got better & better. Now that it's fully burned in all I can say is "WOW" what a huge difference across the board sonically.
I've also read about a few easy mods that crank things up a nother notch with this dac. I just might try replacing the stock op-amps with Burson dual HD op-amps. From what I've read this is a very easy mod that reaps huge benefits. I'm thinking about it for sure.