Although I just spoke to the dealer, seemed to suggest it would sound better on a very clear open speaker than a speaker with a dark character.
Hmmm...I'm not familiar enough with the speakers you are considering to comment on them specifically. I can address this comment to some degree, though. The speakers I use I would say fall into the category of a very clear open speaker, where the character of the speaker is completely uninfluenced by the material of the box they are in. They sound great with the KWA150. I would say Daedalus, which also sound fantastic, are entirely different in their approach. Perhaps they have more of a character that is somehow sympathetic to the materials used...a fleshier, richer sound in some ways, not unlike a musical instrument. AudioMachina is extremely clean and detailed and yet not at all cold or overly analytical in delivering the music that way (I say that because it would might normally be what I would have expected). Both occur to me as extremely enjoyable and engaging pairings with the KWA150, yet they do sound quite different from each other. Both are entirely engaging and let the music come through Daedalus with perhaps a bit more "influence" in a manner of speaking (but its a very fine influence indeed). So I would not necessarily limit my choices unless you happen to actually prefer one over the other, or if the music you listen to is suited better for you by one over the other, to your ears. I guess I wouldn't let a dealer, or anyone else, dictate that since the amps you are considering are more versatile than that in my experience. It seems like the dealer is just filtering a personal preference, which there is nothing wrong with doing. Good luck with your quest.