It simply doesn’t compare to Austin, that’s for sure. I’ve never seen Nashville.
That said, it’s certainly better than Houston or San Antonio – so if you’re looking for a big city with some sense of a music scene, Dallas is a good choice. (At least, in Texas)
I’m trying to find words to effectively express why Austin would be a better choice, but it’s simply that they have a special culture about them that Dallas simply doesn’t have.
It kind of like comparing New Orleans to Baton Rouge for food. Sure, Baton Rouge has some pretty good food joints; but it they just don’t have the culture and the style of New Orleans.