I guess all three of us are curious about the AMG HPA.
I have not heard the AMG HPA nor the PRA-9x. I have, however, heard the DAC-9x. I first heard it at an audio show where it was driving a pair of STA-9X mono amps and $25,000 speakers. I was very impressed. I didn't need another amp <already owned the Evo STA> nor did I need new speakers, so I decided I'd like to try the DAC-9x to use in my bedroom. It sounds great!
Sometimes, I wish I could persuade Jason to send me a few components so I could mix and match them to find my favorite combination. I'd keep the favorites and ship the rest back. In reality, I'm pretty close to being maxed out with audio gear, and I am pretty darned happy with what I already have.