Upgrading from Primaluna

Good gear vs expectations vs small room and that buildout on the right side.

You've got challenges. Don't expect demo room performance.

I would try the 1/3 concept.  It's free and most certainly, Sopras WILL sound more "airy" 4-5' out. Your seat will be approximately same from rear wall. Embrace(almost) nearfield listening. Less room interaction.

Now tapping out. I have no qualifications in room acoustics/physics.

You're doing haphazard room treatment without the mic/computer exercise to verify what you think you are or are not missing.

I have the PL300 and the 400, running in mono block with Tannoy Kensington and Avant grade DUO XD; if I were to do it again I would buy the 300.

The 400’s offer so little more than the 300s, at a huge expense if you change tubes.

I listen to your speakers with a Diablo 300, just magic combination; I also listened them with a Pathos Heritage, great combo but not as good as with the Diablo 300, the Heritage had a little trouble driving them at low volumes so they did not sound big and relaxed. I auditioned your speakers vs the Tannoy at Upscale with a 300 and 400, the PLs just do not have the drive these speakers need. For the PLs you need 90+ efficiency especially if you listen at normal levels then you can get the best out of the amps. to my ears the 300 drove the Focal better than the 400, but that is my ears, which did not know if it was a 400 or a 300.

If you want to add some tube color get a tube preamp, your speakers are not easy to drive, especially at lower volumes, they need the power to open up and then they are very nice speakers.

Pardon my English, not native :)

Definitely get the speakers farther apart and toed in more.  It costs nothing.  Move your listening seat forward to create an equilateral triangle, you can move it back a bit, =10%, later.  Don't know how the PL sounds with your speakers, you could ask that crazy guy on the West coast for advise.  PS audio gives you a free trial period so no risk to order.  That SS amp will sound very different than the PL.  This may not work... but, can you move the speakers to the long wall?  May be a real improvement if it can be done.

Have fun!

Also, want a cool running amp?  Try PS Audio's Class D mono blocks. My Wilson dealer tells me he's got some customers with big Wilson's running them and they sold pretty good.  A reasonable endorsement.

I own a PS Audio 250 amp and matching pre amp and I am very happy with the sound. My speakers are floor standing SF