over the years my take on the Lamm presentation is a slight darkness, but not closed in or particularly warm, caramel colored or rolled off. and great bass for sure. this compared to a few other tube amps i've had in my system over the years; starting with the Tenor 75 Watt OTL's, later the Berning 211/845, then the VAC 450 Statements.....which (the VAC's) were more lit but also caramel and more rolled off.
the best analogy would be how my Transparent Opus MM speaker cables sounded compared to my Evolution Acoustics TRSC (triple run speaker cables). my EA cables presented a well lit soundstage, the TA a bit dark. but not soft or rolled off. just the degree of light. the Opus MM is an awesome sounding speaker cable.
i hold the Lamm amps in very high regard and hope this not taken as any criticism, as it's not my intent. i do think this slight darkness does seem to synergize with naturalizing some bright leaning tweeters. i hear that too.
obviously my reference for a naturally lit presentation is not only the tube amps i had, but also my darTZeel. i'm sure i'll get a bit of flack, but i do think this is what is going on.