The iBasso AMP14 uses one 6th generation triode Nutube 6P1, also found in the AMP13, as a voltage amplifier but now is followed by a JFET differential converter to realize a differential output.
iBasso AMP14 adopts two JRC volume control chips which form a total of 4 channel true balanced volume control.
The signal then passes through the 4 channel balanced output buffer stage to give 5.2V RMS from the 4.4mm headphone socket while there is also a dedicated balanced line output with 1.8V RMS, which is much lower than the 4V industry standard.
In case that you need a full scale 4V balanced line output then you should consider AMP12.