MF Sushi is an excellent, albiet probably overpriced sushi place within walking from the Hyatt. They have all sorts of cooked stuff as well, but prego wife might rule that out.
http://www.mfsushibar.com/
Bistro Niko is an upscale french place within walking of your hotel.
http://www.buckheadrestaurants.com/bistro-niko/
It is solid and not too pricey. Probably your best bet. You need a rez though. Make one now.
If you would rather try walking from the Fox I would go with Livingston. Also probably a little overpriced but pretty good.
http://www.livingstonatlanta.com/
Empire State South is also somewhat near the fox. It is excellent, but probably too late for a rez unless you wanted to do the super early 545 before the show or something. Its also probably 8+ blocks to Fox so wifey might not want to hoof it that far.
http://empirestatesouth.com/