From "Wrecking Ball" forward, Emmylou has some nice recordings, though after the follow up, "Red Dirt Girl," I've not been grabbed by the music. I prefer the "new age" Emmylou recording the older recordings I've heard, including the well-regarded re-issue of "Luxury Liner."
I'll definitely checkout "Songbird," which I don't know.
Lucinda Williams cares about sound, and has some good recordings: see especially the "delux edition" of "Car Wheels" (musically, the album is a masterpiece, IMO).
John