Rock solid! The LCD-4 sings like a beautiful peacock on the LP, which knows how to make the 4 sing, with all the various lights and shades of its dark gravitas : well extended, and textured lows, thick creamy stately mids, all crowned by spacious, airy details. I see no down sides at all, in the set up I've described. Of course, other links in the chain of components would matter as well as usual, including the types of music you listen to, although the combo does well with all types of music I throw at it. Still, I tend to think that, because the LCD-4 already hits hard and deep in the low end, it might probably not be ideal using tubes for it that emphasize the low end too much, because things might go overboard a little bit, unless of course, one is an unrepentant no holds barred bass head, in which case all bets are off any way.