the smoothest sounding speaker

Ozzy, tell me about it. I am also looking into Dynaudio MC15 active speakers too. They use A/b amps. No Flying Mole digital stuff. Then all I would need is to build a dual mono motorized Alps pot volume control. The Marantz CDP is sort of harsh although really good for the $$$. Such a bummer the Sony SRP-P50 is no longer available. I also like the Creek A50r. Can't find those either.
I have built a variety of single driver speakers and even though they are fairly low resolution they are still harsh. That's because of the breakup modes, typically at 6 and 12kHz. No wonder people don't design these drivers into speakers to run full range, even though the driver can do it.

Zapper: Which Silverlines do you own? What do feed them with? I've heard several models at HE shows and always enjoyed them. TIA.

Ohm Walshes. Utterly non-fatuiging, with great transparency, imaging, and sounstaging. A no brainer.

Focal 1037 BE. (aka JM Labs) When combined with Virtual Dyanmic cables they are very detail but non fatigue. I have the 1037 with the beryllium tweeters and VD cables (all round), i can listen hours and hours without any fatiguing at all. The

I will caste in a reference to the ACI Sapphire XL, a speaker that is very similar to Aerial Acoustic's in the top end. They are certainly the type of speakers you can listen to for hours on hours, even on transparent transistor amplifiers.