The operating theory has been for a while that the quality of a recording is an accumulation of subtleties. Which is why listening to any given preamp makes you think "Huh, that sounds pretty good." Even cheap preamps in (say) Mackie mixers.
But remember that mic preamp shootout a few weeks ago? Yeah. The differences between the preamps were pretty apparent. At the same time there really wasn't a correlation between expensive and good. In fact, the cheapest preamps were among the best-sounding.
The ART PRO MPA II is... well it's just amazing. The sound is (to use a real weasel term here) rather 3-D.
I compared the direct-injected sound of Alice, the Fender Squire Jazz 5-string, between the ART and the built-in preamps in the Focusrite preamps in the Scarlett interface.
The subjective difference is that the Focusrite were more, er, focused. And the ART were more broad and deep. Actually I'd say the Focusrite's were more accurate than the ART's. But that's cool. The ART preamps have plenty of color, which you'd expect from a tube preamp.
§As an old man I've started to get very grumpy about audio engineering. My grumpiness is suchly: once you've got gear that actually works, it's all pretty good. Spending untold amounts of money on esoteric gear isn't nearly as helpful as, say, practicing your instrument.
Maybe this wasn't as true back in the day of Realistic mixers and those early Tascam mixers. Because I had a lot of trouble getting those to sound good back in the day (mid 1980's).
But now I have Neve preamps and Apogee converters. They're not night-and-day better than even the Focusrite built-in preamps and converters. Not even dawn-and-dusk better. Arguably not even better in all situations. Am I contradicting myself here in the last paragraph? Yes. Yes I am. Just a little. I'm like the New York Times. Don't worry about it.