The Duke Energy Theater is found inside the Spirit Square complex uptown - so you might not know it from the outside. When people refer to "Spirit Square", they most often think of the McGlohon, which is a whole lot nicer (and larger).
The Duke Energy Theater, on the other hand, is a nice space, but it is on the small side. It is in fact so small that if you are near the front and you catch a spirited (see what I did there?) performance of say "Die Roten Punkte", the movements of the performers can be felt through your chairs. Most larger venues just don't convey that - and they probably have much nicer chairs too.
On the upside, it's a very intimate space, even smaller than the Booth. On the downside, it's not the most comfortable place to see a lengthy show, so hopefully you won't be sitting for long.