My Big Six is involving, but to me not at the level of the L4's musicality, at least not yet. I've got about 200+ hrs on the Big Six and it's more of a "grab you by the throat" kind of DAC that has awesome resolution and can delineate images that the L4 left blurred, especially with complex passages. If it can float music out there instead of projecting it then the Big Six will probably be the last DAC I have. I'm hoping it has the 3D gene in its DNA...
Interesting observations. Do you have Duelunds in there? Take forever to break in. Old man Glory may be right about the tube selection. Time will tell.
Another capacitor alternative to the Duelunds that has appeared recently is the Jupiter Copper Flats. http://www.audiocircle.com/index.php?PHPSESSID=0msk4f3cesm5tc1u0edukpsis3&topic=119876.msg1261678#new