What differences did you notice in the dac with the caps? How did you try it, replaced and got back the dac each time?
The Duelunds took 4 weeks to settle down, but right from the get go they were obviously smoother and more natural than the V-Caps in before. The V-Caps replaced Audio Note Copper caps (standard fit), which to my ears sounded thick, slow and restricted in frequency range and detail. The only thing I liked about the coppers was the mid-range. With the Duelunds you get better midrange, PLUS wide bandwidth, massive soundstage and deep and powerful bass and sub bass, and detailed and smooth treble. As I said, the best of both worlds IMO, bass and dynamics of the V-Caps and fantastic midrange. They are also 'slightly' warm which helps in a DAC I think. Teflon caps can sound a touch cold.
I have excellent aural memory and had used the coppers for 3 months, the teflons for 8 months, and the Duelunds now for 4 months. I am convinced by the Duelunds. They are not cheap, but they can change the sound to a bigger degree than almost any other tweak or tube rolling I can think of. They can basically transform a DAC or amplifier.