I have heard the Wilson Benesch Arc many a times. Sure they have gone ahead tried new materials in order to get rid of unnecessary coloration. But then they have gone a bit too far and actually cleaned up a bit too much IMO. Some of the real musical harmonics have gone missing with that speaker. It is something thats very common with many of the current ultra clean audiophile sounding speakers.
Pani, I think you're confusing box resonance/coloration for musical harmonics, as if the box material is editing out the content of the music. IMHO, that's nonsense. Now, if you want to debate "colored" sound vs transparent sound, that's an entirely useful debate - for some people, they don't want completely transparent reproduction of a CD/LP's content. "Colored" sound can be very helpful, as I pointed out in my last post, when listening to badly recorded material. You just have to decide what you're after.
For me, all I want is the music as clean as I can get it. Saying music is too clean, for me personally, is like saying you cleaned a glass table too much - there's no such thing. It's either clean, or it isn't. But then, I also own a pair of older Sonus Faber Concertino speakers - a great example of beautiful sound reproduction, but colored in that warm SF way. Again, it's all about preference, and what makes your ears happy in that particular listening space and your chosen music.