I was very surprised to see the gain controls positioned in the back:
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If you use multiple headphones with very different sensitivities, this will be an annoyance, having to reach back here to change settings. Fortunately for the set of headphones I use, the medium gain was sufficient.
FYI company claims that there are 99 opamps used in the P2! They must be paralleling a lot of them to get maximum output power.
I put the amp in high gain mode, fed it from my RME ADI-2 Pro DAC, and set the volume quite low. I nearly fell off my chair when I hit play! The sound was so loud that I had to rip the headphone off my head. The gain is quite high in high gain mode so even low volume settings is liable to create high loudness despite me testing with my insensitive Dan Clark Stealth headphone (XLR out was used for all the listening tests). I set the gain to medium and that was plenty loud to drive the Stealth into distortion.