What preamp are you using with Primaluna Dialogue Premium HP amp?

That link is the 8ohm tap here is the 4ohm, not much better and still behaves like a tone control.
https://www.stereophile.com/images/1116PLPPfig02.jpg

But its sonic signature will be far from neutral, especially with lower-impedance speakers.—John Atkinson

As for the Kantor simulated load being as you say "quite severe"
" The load is "moderately" demanding but not untypical John Atkinson".

Just to give you an idea, what the Kantor simulated speaker load is and how it measures here it is, notice the impedance dips at 200hz and 4.5khz. And peaks at 65hz 1.5khz and 10khz
Then look at the frequency response (black wavy line) of the Prima Luna in my last post, it can’t supply power into this hence mimics this Kantor load with it’s uneven frequency response by + - 7db!!
https://www.stereophile.com/content/real-life-measurements-page-2

Cheers George

arch2 OP

The "black wavy" line is how this amp behaves (frequency response) into a not too severe Kantor simulated speaker load. As you can see it’s got plus and minus 7db peaks and dips, you need to "counter" this if you wish to have nice flat frequency response.
https://www.stereophile.com/images/1116PLPPfig01.jpg

I think one of these between preamp and poweramp or between source and preamp, will work out very nicely to get a good flat in room frequency response.Then you can "counter" the peaks and dips. https://www.schiit.com/products/loki

This is why it’s always better to get a poweramp that stays close to flat in frequency response with simulated speaker load.

Cheers George