Dallas got its first opera house in 1883 (GC5AFBT), which was in use for 18 years before it burned down. Work began at this location almost immediately. The new opera house had 2 balconies and 6 boxes, seating a total of 1,800 (up from 1,200 at the old location). The building of the opera house helped establish this site as the social hub of the city. Hosting many of the leading actors of the time, the house flourished as one of the finest theaters in the South. Unfortunately, as did many of the early theaters, it caught fire and burned down in 1921. A few years later, the site was purchased by Titche-Goettinger, who developed it into the building you see today.
Coords are kind of tricky here so I'll get you started out with some help. You're going to be not far from the SE corner of Main and St Paul, and near the sidewalk. Coords confirmed on Google Earth.
Side note: this was my most expensive cache to date. Reminder: when grabbing your caching tools from the car and taking them to a site, be sure you have your keys with you so as to not NOT lock them in your car. Locksmiths are VERY expensive :-)