"OP: I have no idea how he does it but the designer truly achieves a sound that is uniquely detailed, smooth and imminently musical"
I believe it may use the same "Pleasure Control" (volume control) as their flagship NHB-18NS $25k preamp below, which is an LED/LDR series shunt volume control which has no switches or contacts in the signal path, as all normal volume controls have.
"DartZeel NHB-18NS: A whole new volume control module, which completely avoids the use of any potentiometer, stepped attenuator or analog switch array in the signal path. The sound signal is attenuated in a fully passive way, using special analog optical couplers"
Cheers George