To be true only a very very few people can detect properties between well designed amps. I am very skeptical to opinions like "bright", "bass slam", "sound stage" etc. etc. Those people normally don't have any reference gear besides the amp in test so they are listening to the whole chain and have no idea how the amp itself sounds like.
I have listened to PPA, not much though, and it sounds good, equally good as mine. When I listen to my 7 different amps I can't detect any significant difference but since I have designed them it's a certain feeling for each of them.
When it comes to QRV08 people that have listened to it have loved it. Noone yet has built one but two may be built in the fall. You should not build this amp as your first SMD project unless you have a very good selfconfidence AND are handy.... but if you do deside to build it you have one of the most advanced headphone amp in the whole market, DIY and commercially.... says I
No amp in the whole world has ever had 4 super regulators and I'll doubt even 2.
I can say so much that I'm very pleased with the design and I regard this the highest, the best I ever have done. It was very fun to do because each part were already debugged. The amp is a developed version of QRV-06 and the power supply is JSR03 and JSR05 converted to SMD parts.
All amps of mine can drive any headphone you like to painful high levels so you don't have to worry about your Grados or whatever.