How old is too old for a Dac?

The Redgum sounding very good doesn’t surprise me.  Solid engineering principles are to a large degree timeless.  Well thought out robust power supply and  quality analog output stage are essential to obtain upper tier sound performance. 
Charles 

Jond,
I'm not surprised that the Audio Note is impressing you,  it has been highly praised for many years.  Excellent design and implementation withstand  the test of time. No doubt that using Duelund CAST as my output coupling capacitors improved the Yamamoto DAC further.  I'm certain that I'd be just as impressed with the AN DAC as you are. Congratulations. 
Charles 

H I Jond,
What differences are you hearing via further listening to the Audio Note and the Yamamoto DACs?  I'm assuming this was a fun and informative comparison. 
Charles 

500.00 dollars? Extraordinary value. This small Japanese company flies under the radar outside of Asia.
Charles

Jond,
This should be an enjoyable shootout and I am interested in your outcome. 
Charles 

Jond,
Honestly either way you can’t go wrong. It was the tube aspect of the AN DAC that grabbed my interest às well as their reputation. I hadn’t considered Yamamoto until the Distributor expressed such enthusiasm. He was a fellow SET aficionado and had very good taste and ears. Anyway it worked out well for me.

The Yamamoto YDA-1 tubed version is likely closer in character to the tubed AN DAC. As you probably know,  6 Moons did a really fine comparison review of the two Yamamoto DACs (solid state and tube). The AN should be an excellent fit into your system. 
Charles

Hi Jond,
I gave very serious consideration to buying a used Audio Note DAC. At that particular time the then Yamamoto U.S.distributor (Venus HiFi) had been a longtime Audio Note dealer. He was extremely impressed with the new Yamamoto YDA-1 DAC. He told me that you’d have to get a AN level DAC 4.1 to equal the Yamamoto.

I trusted him and got the much less expensive YDA-1. I suspect that I’d been happy with the AN DAC as well. That was 8 years ago and I’m still very satisfied. Your mentioning the AN 3.1 Signature DAC brought back that episode. No doubt your AN DAC is terrific! I did install Duelund CAST output capacitors about 6 years ago. It went from excellent to superb 😊
Both companies pay much attention to the power supply and analog output stage quality. Both also avoid using opamps in their circuits (for the same explanation, no negative feedback wanted). Both DACs have stood the test of time.Jond I  don't believe that it's coincidence that both of these manufacturers also built SET amplifiers.  They applied the same principles to their respective DACs with obvious success. 
Charles