You have to go to a major population/cultural center to get what you want. Since you are doing studio work and your future wife is in theater, there are really only a few choices. The prime choices would be New York City, Los Angeles, and Chicago. Really, it's between NYC and LA in my opinion if you want to be in a major market.
I'm a musician and composer, and have worked in theater in LA, Boston, Chicago, and a bit in NYC as well. Theater in LA is kind of spotty as far as making a living from it, but there is a lot of it. This is a TV/film town. NYC is definitely the center of theater in the country, but in LA your wife would also be able to audition for tons of TV/movie roles as well. If she is strictly interested in theater, then NYC would be the place for sure. Chicago has a great theater scene as well. But in Chicago both the recording and theater scene is smaller than NYC or LA, and is more insular.
Then there are are cities like Boston and San Fransisco. Both are great cultural towns with a recording scene and theater, but less known for it than NYC or LA. Perhaps more enjoyable though in terms of being nice places to live, but smaller markets with less opportunities. In Boston though, your wife could easily pop down to NYC for auditions, a lot of actors do that.
Having grown up in the midwest myself, I started out in Boston, then moved to Chicago and now live in LA. Sort of gradually moved up to larger and larger cities! NYC and LA are definitely the biggest markets with the most quantity of talent, opportunities, etc., but other cities may be perfect for you, too. I'd suggest taking a driving tour across the country and plan on spending at least a few days each in the cities you are most interested in. That might be the best way to find out which town 'clicks' for you guys. You might get that moment when you both go "this is the place!". At least, that would make it easy.
