Ok, I went ahead and got the NX2
The first impression is a little of mixed bag. Not very impressed I am.
The noise floor (HISS) from the amp alone can be clearly heard with the Zircons and some other IEMs. I guess the NX2 is not meant to be used with sensible iems after all. The amount of HISS is comparable (almost identical) to the one coming out of the Ipod Video 5.5g
So, sensible iem + NX2 is a no-no which is a pita as this means you cannot use it as a DAC with them. This is somewhat a show stopper for me. To get rid of the hiss, you need a can with about 32Ohm impedance. My old PX100-ii is a good example of such headphone.
Using a less sensible can (HD598) the hiss goes away. Good thing is the NX2 has plenty of power to drive them. I find myself keeping the volume knob between 2 and 2.5. Going up to 4 becomes uncomfortable.
When using the NX2 as analog amp for an Ipod Touch 5g you can feel there is more power. Bass is more present however it also tends to color the mid-bass region too. This is specially noticeable with acoustig guitars. In a word the music becomes more "melodic". Female voices appear unaltered. Highs are less detailed and less present.. Transients here "smudge" a little (specially cymbals). String instruments (ex. guitars and violins) become more smoothed.
Connecting the NX2 to a Fiio X3 2nd confirms the impressions with the Ipod. The bass overflows its boundaries and higs become less detailed. The power is there but marginally more than what the Fiio is able to put out by itself. I have not tried with really hard loads but there's no point using a $40 amp with a $500+ HP. Basically, the X3 is better alone with no NX2 behind.
Used as a DAC it is recognized in both Windows 10 and Mac OSX. No new drivers necessary. The hiss is still there, so you still cannot use iems. However, the sound becomes more neutral and less colorfull. I would say it becomes as it is supposed to be.
I guess I must say that "for the money" it is OK. Probably more than OK. It is small enough to be stashed in the headphone pouch and forget about it until needed
At this price point the NX2 is also a good donor for a DIY upgrade hobby. You can open it and play at will upgrading stuff and playing with the soldering iron without felling too guilty.