Hello,
I have just received the S17 yesterday, my current AMP has been Singxer SA-1 V1 combined with the ARES2 DAC firmware 1.8. My primary headphones are VERUM 1 MK2 with 7 ohm of impedance.
After few hours of listening yesterday night, I need to admit, S17 is not the upgrade by one step compared to the Singxer, it is an upgrade 2 steps up or more.
The price difference between the 2 amps is absolutely ridiculous in the US. In the Europe is much wider 430 vs 699. Anyway, for 700,- S17 is no brainer and the bargain. Best AMP I have ever heard period.
The sound of S17 is effortless, under full control, mellow, clear, the TUBE effect is there, however, your experience might differ with your specific audio system.
I would not use the S17 for the high impedance headphones, even though, it claims a lot of power in that impedance range. I would look at some dedicated high impedance headphones amps. I see the S17 as an ideal choice for the planars with the low impedance.
The unit is not perfect though, the volume knob is a disaster, you do not want to touch it, I control it via the remote which works great, LCD screen is quite basic with poor view angles, there are almost none vent holes, usual temperature is 55degress at 50mA. On the other hand, the overal build is solid with the quality neutrik connectors. Almost all the money went into the electronic components of the device, nobody should expect a perfect chi-fi device for 700,- btw. the preamp out is always on and S17 does not have any standby button.
It is a keeper for me, Singxer has been dethroned in the price range by a lot of margin.