Why do records made from digital sources sound good?

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.

Whenever folks reference the colorations of analog / vinyl, there is usually a connotation of superiority to digital / solid state AND to the listeners who prefer their sound "clean, untained".

I readily admit the colorations of viny playback gear & tubes BUT sincerely find them - in the appropriate amounts and combinations - to be wonderful! A true testament to the way our universe sometimes expresses beauty in unexected and nuanced ways. Plus, the endless mix & match combinations make this a hobby worth sustaining for more than a week. 

Somwhat related is the usual whipping-boy of "dynamic range compression" in recordings. Yes, too much is bad, and a recording explicitly mastered for car/portable use is much more likely to sound just plain bad. BUT too much range is bad too - I DON’T want to crank up volume to hear intelligible vocals, just to have a snare drum hit pop out my eardrums! The proper mixing for a home environment is an artform of its own, which combines talents of artists AND mastering engineers. When done right, the playback in your system is a kind of performance in its own right. NO, it is never going to be the same as live, and with many kinds of material it shouldn’t try to be. That’s why the extra dynamic range capability afforded by digital is often meaningless in practice. Vinyl has "enough" for most use cases.