I've heard these both several times at my dealer. Although not side by side and I wasn't critically listening, it's just what he had hooked up for various demos for other clients. Part of how they sound will also depend on your room. If it's smaller, the Atria maybe better in some respects. The Avior is slightly more efficient, so this may help with your amp.
The midrange, it's a Rockport after all, will be similar. The bass, mid bass is likely better on the Avior, again this can be room dependent, one can be to much (or to little).
You won't go wrong either way, and I do think your room is really the determine factor about which is better.
You won't find a better speaker at either price point. Well set up, these are special speakers.
Good luck