Why do records made from digital sources sound good?

I think perhaps the answer is the same as why do tube preamps make everything better?

I am not saying everyone feels that way, but it's certainly true for many.  Regardless of the source, analog, tape, digital, a tube preamp could be the sugar in the coffee you always like to add.

The phonograph playback chain may be the same for you. 

”Sounds good” and “sounds better” are totally subjective judgements so anything is possible.

There are tons of spectaculary bad analog and digital recordings. Also, spectacularly good ones. In part it depends on when they were made. In the late fifties most of the finest recordings ever produced were made. They were all analog. But during that period there were still some spectacularly bad recordings made. The tinniest horrible brittle ones, typically early rock, but I’ve heard some horrible classical as well..

Then the industry slowly switched over to digital mastering. Wow, there are some terrible early digital recordings. Deutsch Gramophone, known for outstanding classical recordings produced some incredibly bad stuff... released on vinyl. Over time digital recordings got better. But the digitall playback systems got better as well... only in the last ten years of so have they equaled vinyl playback.

So there have been long termed trends, but huge local variation within the time frame for recording, then the same in playback.

Today, the playback equipment has erased (or can, if you have a good system that is carefully curated) any difference between analog and digital. So, then you are left with how they were mastered.

billstevenson

... how can a digital master, for example make for a better sounding record? ...

If it's a truly hi-res digital master and great care is made in making LPs from it, it's possible for the LP to have a much higher extended frequency response than a CD made from the same master. That extended HF can lend a sense of "airyness" to the sound. 

I came to the conclusion that it simply comes down to:

1. The mastering quality.
2. A personal preference for the additive distortion components of various phono cartridges, step-up devices, and phono stages.

There’s nothing magic about vinyl itself; it’s actually an extremely difficult media to work with. But for various reasons, it’s been positioned as the "high fidelity for the masses" medium during both its salad days and the more recent revival. CDs, unfortuately, were shoved pretty quickly into the "car and portable" majority use case, and their typical mastering quality reflects this. The culture was shifting very fast at that time.

Early CD reissues of older material suffered from poor understanding of mastering techniques for digital. Then very quickly, the audiophile was no longer its main use case. And at some point, the original master / recording tapes for older material either degraded or were lost. Through all of this, older pressings of vinyl enudred, in all their glory.

With new pressings of new material - I agree some of it (actually, a LOT of it) sounds great on vinyl. But it can sound equally great on digital too! They can make these sound a lot alike, if they choose. For what it's worth, I have a few "all analog processing" pressings of modern material, and they still sound the best. Can't fully explain why, but they do (probaby, I like the added warmth of the master tapes!). And a well-done 45 RPM 12" always sounds a bit better, too. 

The digital quantization and DAC conversion process was NEVER at fault. As you discovered with the Suger Cube, these processes are actually VERY transparent. I’ve even piped my high-end vinyl sources into a Meridian 808i DAC/preamp - which digitizes on input and the DAC-converts on its outputs - and the output sounds 99% the same. The quality of mastering / engineering is the greatest arbiter of sound quality.

And yes, I DO like the sonic quirks of certain cartridges and phono stages. They have their own personalities, just as we all do. I am NOT in the "absolute sound" or objectivist / measurement audio camps.