If you're interested the Essence STX II, I'm assuming music quality is your primary focus (otherwise you'd be looking the Strix). If there are various dedicated sound cards out there for people to spend extra money on, then you can bet more quality is possible.
Recent generations of ROG motherboards have brought audio quality to an exceptional level already, the codec and DACs rival even some prosumer solutions. Assuming you have a good amp paired with those quality speakers, you should be very happy with what you get from any of latest ROG motherboards. If you are an audiophile who has invested an exorbitant amount money into your headphones, audio equipment, and cables, then you should seriously look to the Essence for even more detail and quality. To experience that, the right equipment to match is essential, naturally.
This decision doesn't come without caveats though, your graphics card becomes a factor due to interference, so it's important not to place the Essence right next to any of the latest high-end cards (farther the better). Also there are some platforms you'll need to avoid (more info below).
https://rog.asus.com/forum/showthread.php?101937-Essence-STX-II-and-STX-II-7-1-incompatible-with-X37...
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