A Digital-to-Analog Converter is meant to provide us with an analog sound and R2R DACs do this better than any other type by a big margin.
They offer excellent timing, accuracy, low jitter, and linearity without the need for digital correction, processing and filtering that you find in Delta Sigma DACs which often introduce errors and sound noticeably “digital”.
If you enable HDR and oversampling of the fc6 and adjust the options and filters you will notice that it sounds like a Delta Sigma DAC because it uses digital processing.
R2R DACs tend to produce a warmer, smoother sound without losing any detail, and the sound is significantly denser.
IEMs play a crucial role in the sound quality as well if not the most important!
When I tried them with a set of full BA IEMs the sound was very cold and analytical which I didn’t like and so I sold them.
With dynamic driver IEMs the sound tends to be warmer because pure DDs tend to give you the sound of the source .
I don’t notice any roll off as it extends beyond the hearing capabilities of human ears.
You can test this yourself using a simple frequency generator app you will hear frequencies from 30 Hz up to 18 kHz.
I got this device a bit late but for me this tiny device sounds better than any Fiio DAP just to make it clear.