Tried my quad of Tungsrams in the LF, and they do definitely add some solid weight over the stock tubes. Maybe over the Siemens too, but the Siemens sound tighter and there's a wee smidge of glare or grain on some of the upper end on the Tungsrams, whereas the Siemens seem to have some of the bright tones but not as etched. This is REALLY preliminary hearing stuff (my power went out for about an hour, which cut into my listening time) and both quads are NOS without much break-in, so take that as a massive caveat. I've rolled the Siemens back in and plan to get them some good ear time in the next week or two, then maybe switch to the Tungrams again and give them more time to settle in as well.
Though reiterating what has been said before, the LF is very revealing. Folks who've heard my music can attest that the mastering on a lot of my music tends to run on the hot side, which is part of the reason I tend to err on the side of warmth and weight when changing my rig. While the LF doesn't make the hotter recordings unbearable for me, the style becomes very apparent when compared to a more "evenly" engineered and recorded piece.
It also has this wonderful effortless quality to the texture of the music. I've heard amps that may image better or have a better soundstage, but I've sometimes found the presentation artificial or forced. There's space around the tones and instrument voices that I'm hearing, but it's also all still enjoyable as a whole and interweaving sensation.
I'm holding off on really getting "critical" or complete A/B comparisons until I get more time to adapt to what the LF is giving me, but there will be a more in depth impression sometime in the future. Especially when the Siemens and Tunsgram tubes have time to relax into their full glory.