Grizzlybeast has an extensive review on Head-Fi of the Nuprime HPA-9 amplifier. He loves the pairing of the HPA-9 with the Fostex THX00. Don’t forget that the THX00 is currently available on Massdrop until 4/1/16.
Pros: Nice bass, not harsh or sibilant, Great sound
Cons: could use a little more airiness