Upgrading from Primaluna

…Those other posts are full of assumptions

respectfully I would submit that determining the SPL and maximum power the OP is using currently, would be germane as to whether more power is needed.

Like the OP, I too have a Dialogue Premium HP. It seems to pump out 90 dB(A) as measured with an iPad NIOSH app, at ~9’ in a room that is big in spatial volume… and it sounds “o’roight” doing so.
And my speakers are perhaps a bit less efficient than the OP’s??

There are 2 problems with those Sopra 2 speakers:

1. The load is a bit difficult to drive as. It is low impedance and also the phase angle gets high.
2. The distortion is low, which is good. So they tend have a bit of a quiet sound, and to me they begged for the volume to be turned up.

(When I heard them, they did sound great.)
Hence - with the combo of 1 & 2, I would probably upgrade the amp first.

I assume that the OP is using the 4 ohm tap?
They may also benefit from a set of KT120s if they wanted to keep the PL amp.
Maybe that would allow them to punch a bit harder?

You could consider upgrading to a newer PL setup.  I bought EVO400 separates last fall, and I fall more in love with the whole rig every day.  Hoo whee!

2 ft from the side walls sound correct. However, that measurement should be from the tweeter or center of the speaker...not taken from the outside edge of the speaker. 

And yes, do add diffusion/absorption on the front wall and look at the ceiling as well. These will make the speakers 'see' your room as bigger.

Think of the front 1/3 of the space as the highest priority to 'soften' and diffuse.

I had my Evo 400 running my old 88db 6ohm Salk speakers on the 4ohm taps for years before I tried the 8ohm taps for kicks. Upper treble and mids were much better with 8ohm taps with no adverse response from the bass. I could have kicked myself. I assumed because the Salks dip to 3ohms that the 4ohm taps were the way to go.

If you run the numbers, the DPHP should have enough power to push your speakers to ear damaging volume cleanly. I used mine with 87dB Dynaudios until I moved on to more efficient speakers. Having options is good though. A solid state amp could be a nice complement to the DPHP, even if it’s more of a lateral move than a clear upgrade. Sorry I don’t have any recommendations though. I went for low power Class A which wouldn’t have enough grunt for your situation.