Just rolled the Russian EH 6922 into the DAC-11.. been listening for approximately two hours with the Sennheiser HD580..this tube's got a lovely sound.
The stock tube's bass is more lush & 'punchy' in comparison to the EH tube. The stock tube's midrange sounds a tad more forward. Where the EH tube's midrange is clean, crisp, and neutral, the stock tube's midrange offer more of the stereotypical 'tube flavor' with it's warm, thicker, liquid mids (almost ortho-like). The stock tube's treble is smoother by comparison; the EH tube offers a crisper, brighter treble.
To my ears, gain levels seem even between these two tubes.
mickster1972 described the EH's sound as "accurate, involving, and dynamic".. that couldn't be a more apt description. I'd add 'clean' to that list. Bass is tight, fast.. but has a nice, natural decay. The midrange and treble has astonishing clarity, balance, & detail. There's a noticeable improvement in instrument separation, resolution, & soundstage (the stock tube has a bit more depth, while the EH has noticeably more width) vs the stock tube. The sound from the EH tube is more expansive and lively while the stock tube is a more intimate & 'closer to the stage.'
Tonally, the EH tube's sound is on the cooler, crisp side neutral.. but music sounds very full and dynamic. The DAC-11's famed, uber-'black background' is in full 'show off' mode with this tube too... that's one thing that jumped out at me immediately.. very very impressive.
All this being said, the stock tube is really quite superb. The EH offers more of a different flavor than any kind of glaring, outright improvement, as a whole. I definitely see myself rolling both in when the mood demands.
I've only got a few hours on the EH tube so we'll see where it takes me as they burn in.. but I'm certainly impressed and for the ~$15 or so I paid for them, I couldn't be happier.
Can anyone recommend a warmer, more lush, colored tube (that's in the same price range, <$30) to complement this EH tube? I'd like to have three tubes that kind of complement each other. The EH is one the brighter, more neutral side of the spectrum, the stock tube seems to fall right in the middle.. so I'd like to have a tube to that's warm, velvety, but on par (if not better) from a technical standpoint to the other two.
Thanks to mickster1972 for recommending me the EH, too.