I have had the chance to listen to Q-cap Polyprop vs PIO. This is a very interesting pair of caps indeed. There is a difference. The Polyprops sound modern in a good sense, very good bottom and the upper freqs ar not extremely in the foreground. In an open sounding cirwquit, this makes sense. A very good capacitor, indeed.
But in my ears, the PIO are even a little better, little more open in a very very musical way, but not sharp. Wonderfull flowing and livelike, natural and dynamic.
The choice always depends on the rest of the chain and personal taste , But these are my favourites now.
It´s fun to listen with both of them and I´m really looking foreward to the time, when they are burned in...