Here are some of my initial impressions.
1. Build quality: this thing is built like a tank. It is surprisingly compact in size for a $2-3K headphone amp, but heavy and sturdy.
2. This is a rather powerful amp. Mr. Park claims that it can output 3W per channel on both headphone plugs, and although I no longer own the power-hungry HE-6 to test it to the limit, the amp made both the LCD-X and HD800 play loudly below 10 o'clock (disclaimer: I am using Pure Music dithering volume to -12dB, and a 2V RMS source component). On certain tracks, the headphones start clipping past 12 o'clock.
3. It takes long hours of burn-in before the amp starts singing. Also, the sound really opens up and becomes more transparent past 30 minutes to 1 hour after the power is turned on, when the tubes get warm enough. Even so, the amp itself never gets very hot and doesn't dissipate much heat, unlike my previous ZDSE which also served as a secondary heater in my room.
4. This doesn't sound like any typical tube amp. I would have mistaken it for a solid-state amp had I not known. It doesn't have the so-called typical warm, lush or tubey sound heard in many tube amps (especially Woo Audio). On the contrary, it is very clear, fast and precise, while retaining a wide soundstage.
5. The amp is very neutral sounding, and although some people hate the use of this term, I'd say it's wire-with-gain. It doesn't seem to have a sonic coloration of its own, like many tube amps do. For some folks who enjoy an euphonic sound experience, this amp may sound a bit boring to them; however, for those who seek the truth in sound, this is perhaps as close as a tube amp could possibly get.