There's three different aspects to this question: design, implementation, and results. From a design point of view there may be nothing better since the Distributed Node Amplifier. I don't know, it just seems that way.
In terms of how the exact details of how that or any other design is implemented, well that is a whole other story. Because as stringreen and others notice its not just the design but the parts that go into them. Then on top of that you have to factor in the way those parts are used. Not only where in a circuit but the physical circuit itself. People over time just get better at shielding, the physical location of a circuit, vibration control, all the little details. No doubt this has gotten better.
And then, results. What I think you're asking- how much better do they sound today? To which I would ask: Do they?
In terms of how the exact details of how that or any other design is implemented, well that is a whole other story. Because as stringreen and others notice its not just the design but the parts that go into them. Then on top of that you have to factor in the way those parts are used. Not only where in a circuit but the physical circuit itself. People over time just get better at shielding, the physical location of a circuit, vibration control, all the little details. No doubt this has gotten better.
And then, results. What I think you're asking- how much better do they sound today? To which I would ask: Do they?