I am using the SMSL DA-9, Rotel RC-1572 MKII pre and RB1552 MKII power and the Topping PA5 with SMSL SU9, SU9N and Sanskrit 10th MKII. Whichever combo I use, it gets shouty and bright when I push the volume. Erin who recently reviewed the R100 confirmed what I was saying all along, it is detailed but it can get lean at high volumes. Its no wonder because from graphs, we can see it indeed has a rising top end. Great at low and normal volumes, not so at really high volumes. Still one of the best sounding speakers Ive owned so far, with the 12.2 taking the top place.
I have not heard ANY of the new line of Polks, but have found in general, some speakers that get irritating or lean at high volumes, tend to be just a bit strong in the 2 khz-4.5 khz range.
Often just reducing this range even 1 db or so, will take away that strident sound.
Or it may be as you surmise from listening, due more to the top end sound.