I haven't been this excited in a while!

@dseltz 

I have listened to all the Wilson speakers at a few different dealers and no Wilson speakers ever sounded bright 

First I tried the Alexia 1 and it was a HUGE failure.  It defied all expectations as the bass from my Sophias was deeper and cleaner and they were extremely bright.  They sounded so bad that I could not even listen to them while I waited for a buyer, they were rolled away into the corner for months.  At the time, I had the ARC REF 75SE for an amp and while I know most will say will there's your problem, I don't think so.  I took it with me to pick them up from the guy.  He had McIntosh gear, a 2700 preamp and the 450 x 2 amp.  We listed to the Alexia with his set up and then swapped to my REF 75.  The overall output/volume was identical.  We kept the preamp volume in the same position and both agreed the REF 75 sounded better.  It was more musical.  They did not sound bright in his room.

Wilson and dealers all pointed me to the DAW so I started the hunt and finally committed.  They were pretty awesome for the most part, but still on about 15-20% of material were bright.  This was not just in the triangle, I could be all the way around the corner in the kitchen and still sounded bright.  The bass and overall dynamics was great though.  

Next I was trying to use my own logic and thought if the Sophia are so great, the Yvette are kind of a Sophia 4 so maybe that overall size and driver complement will do the trick.  They basically gave identical results as the DAW but maybe at about 80% of how impressive they were in comparison.  

One dealer told me if I want to continue with Wilson, maybe I should go back to the same era as my Sophia 1 and consider a W/P 7 or 8.  I may try that one day.

OP we have the same experience, I was enjoying my Andra eggleston when I visited my friend house to listen to his Omega Alnico , I was blows as well   How palpable and musically involving they are. I end up buying Omega rs8 just to see why they are so musical  and palpable, and applied what I learned from the rs8 omega to Andra, I was cautious my ears were experiencing sound change, not ready to sell my Andra.And now I both kept Andra and my omega since they are both good speakers. All I did is match them.

Hi Dana, I'm new to Harbeth also. I installed SHL5+XD.2's one week ago. Like you, I found the Harbeth sound to be exactly as described in all of the write-ups. I retired my Thiel 2.3's. To my ear, the Thiel's lacked the natural tone and musical flow I find with the Harbeths. I listen to solo cello a lot, and can envisage the arm and finger movement of the cellist thru the Harbeths. 
My small room (11'x12') is heavily treated like yours. I drive the Harbeths with a Luxman 507Z integrated. I listen exclusively to classical. 
I've been experimenting with speaker placement, starting with recommendations from Harbeth's "User Guide", which is online. So far, the recommended distance from sidewalls and front wall is working well, as is the longer distance from the seating position relative to the distance between speakers. I initially tried Harbeth's recommendation to toe-in the speakers slightly. I switched from that to straight on which gave me a more open sound and better soundstage. That may be due to my small room size. 
I'm confident you'll enjoy your 40's. Thank you for your post. 
Leo

@dhite71 

Congrats on your Harbeth purchase !   I am sure they will sound great.  They measure well and have big, solid bass.   I run a pair of Wilson Watt Puppy 8 and my brother runs a pair of Wilson Sophia 2.  Both of us power them with tube amps.  Mine with a pair of monoblocked McIntosh Mc275, and he uses a Music Reference RM-9 Mk.2.  We both are very much attached to the sound and dynamics of our Wilson speakers and much appreciate the sound of the titanium tweeter.  It would be great to hear from you how your new Harbeth compares to your Wilson Sophia.  I am not sure what amp you are using, but, we are very partial to powerful tube amps with our Wilsons.  

@hjdca 

I have the Audio Research REF 160M MkII mono amps

How would you compare the W/P 8 to the Sophia 2?