How to Solve High-Frequency Suckout in Room?

It's curious that it did not occur also with your first pair of speakers.  

@jetter it 100% did occur with my first speakers, just not quite as much. These two speakers have a much different presentation in the mid and higher frequencies. My old speakers sound muddy by comparison. I think this is why the problem is more pronounced with my new speakers.

To rule out that I had a problem with my gear, I did try swapping speaker positions, swapping the cables, leaving the amp speaker cables as is and swapping the cables at the speaker end. No matter what I could still hear the issue on the right side.

Oh, and I even thought maybe I needed to get my hearing checked!  But I was somewhat relieved when my wife heard the same flaw that I did, and I didn’t even explain to her what the issue is other than I told her to pay attention to the stereo image.  And I don’t hear any issues wearing headphones etc.

You could try extreme toe in where the speaker axis crosses about 3 feet in front of your listening position. You could also pull the speakers out into the room more, In live rooms where you aren't able to do a lot a treatments speakers with narrow dispersion would do better if you aren't married to those B&W. 

Thank you for your response and it's always nice to see pictures of the gear in the listening space.  Your gear is miles above mine so please take this with a grain of salt.

I experienced a similar problem as you are having, switched speaker positions and the imbalance (for lack of a better description) stayed on the same side of my room.  And when standing close to the speakers there was no imbalance.  

I have no idea what this means, but in my case I found that if I stand near my listening position and face away from the speakers, the sound was identical from both speakers.  I eventually decided it may be a hearing issue and by adjusting my speaker position I was able to compensate for the difference.

I have been following your last few threads and remember in a prior thread you emphasized you wanted just a TAD more bass but did not want to use digital sound processing to achieve it.  I've never used any DSP so consider this coming from a real amateur.  But seeing your set up, it's hard to see how you will fit RELs in the room without a major reshuffle of your gear and audio furniture and to also take care of the treble problem maybe you should consider it.  A lot of people swear by it.

I am only speculating, but it seems to cure the treble suck out on the right you are going to need to find a way to create an equal suck out on the left without DSP???  Again, just guessing out loud.

The wall is reflecting too much mids from about 1-4 khz, that makes the highs when you listen to that channel alone seem suppressed. Effectively they are in comparison.  You will even get some mids from the left channel reflecting off that close wall too. You need left / right room response measurement to nail it down.