the smoothest sounding speaker

Ultra smooth. This has held true for both the 5.0s and 6.2s I have owned.

Mating with tubes is almost too much imo.

Robr45,
5.0 and 6.2 what???

for sheer smoothness, I wld think Ascendo Systems line of speakers would be right up there

You have many options, but two speakers that are remarkable for their smoothness are Sonus Faber Cremona, and Zu Druid. The Cremona is a voiced speaker that trades some ultimate resolution for musicality, and the Druid is an intimately holistic reproducer that intentionally sacrifices some of its big brother's extreme revelatory character to retain the warmth and unity of a simpler design. Two different price points, yes, but both can be used with a wide range of gear, including the best.

Phil

in striving to build smooth, detailed speakers i've found that the source is sooooo important. much of the harshness and unnatural sound that speakers get the blame for is often the source component. really good speakers reveal the weakness’ and strengths of the other components. often it's really hard to tell what is the component that is the 'problem'. right now i use an Art Audio tube DAC for listening evaluations.