Finally installed the AMP9 last night after burning-in the player with stock amp for about 20hrs. Listened to a few songs then continued the burn-in process (now with AMP9) overnight.
Initial impression is iBasso did an excellent job implementing the Nutube into such a small space. Thankfully, their amp module has just enough room to make this possible and gives many more audiophiles a chance to hear this modern tube tech.
The Nutube lights up green (instead of the bluish-green of my NT-1 amp) a few seconds after pressing play. There's a brief delay until audio starts playing and same happens if music is paused for longer than a few seconds. The tube lights also turn off after a while if no music is playing, perhaps to save battery life.
Sound-wise (so far), the AMP9 has the detail, clarity, separation, spaciousness, etc I anticipated. Won't go into too much detail (or comparisons) until I get several more hours on it though.
One thing I did note, as some others mentioned, is the AMP9's low power output. Can't say I was surprised since my Oriolus NT-1 amp is also a bit underpowered but it certainly has enough juice for most of my non-planer, over-ear phones. Not sure if player firmware needs another tweak or if this is simply due to size constraints. I only used Android Mango so can't confirm if Mango OS will be different until
@Lurker0 (hopefully) releases another DX150 add-on that's compatible with iBasso's latest firmware. On high gain and close to max volume, my HD598 and Sony Z7 lacked sufficient volume for a number of albums. Switching to the 18 ohm Sennheiser Momentum 2.0, it performed better but I was still on high gain and well over 100 volume so no way there's enough headroom to work with many full-size headphones. Gets even worse once EQ is enabled since it drops volume further in Mango app.
I don't use IEMs but I imagine the AMP9 may be a better pairing for those. Also no way to measure my personal listening levels vs others' but (last time I measured using an SPL meter app) mine peaked at about 85dB.
. I managed to get RRS out, so what is left in there must be just the tip piece. But it's really IN THERE, any hope?