I built the 4.1x recently and it displaced my Lessloss DAC 2000 MkII in my system. The Lessloss was in my system for 13 years, so to me it was an excellent DAC using one of the best DAC chips ever and implementing it well in the circuit.
The 4.1x just adds more of what the Lessloss gave me. I don't listen to hi-res very much (maybe some 24/96 files) so 16/44.1 works fine for me. I find the 4.1x to be very smooth and natural sounding. It is extremely quiet as well for a tube DAC. I think what makes the unit special is not so much the DAC chip, but the use of transformers for the I/V conversion and the transformer coupled output. So no opamps and no capacitor coupled output.
The 4.1x just adds more of what the Lessloss gave me. I don't listen to hi-res very much (maybe some 24/96 files) so 16/44.1 works fine for me. I find the 4.1x to be very smooth and natural sounding. It is extremely quiet as well for a tube DAC. I think what makes the unit special is not so much the DAC chip, but the use of transformers for the I/V conversion and the transformer coupled output. So no opamps and no capacitor coupled output.