One thing I’m rarely disappointed about while visiting theaters is their restaurants. A second nice thing about such places is you don’t need to attend a show to try the theater’s cuisine. Take the HAU (check the HAU article) and their restaurant WAU for example, they hold their program and menu at the same level of quality.
If you are sightseeing around Potsdamer Platz and are wondering where to take a break between two exhibitions and to avoid the too numerous malls, consider stopping at WAU. It is not too far away, you leave the touristy atmosphere in a few minutes and can relax a bit with a good pizza or one of the daily dishes.
The restaurant is facing the elevated railway U1, unfortunately not the canal, but the pavement is quite large and some bushes or a temporary art installation will make you feel protected from the street. The tables outside are a good spot in the late afternoon during the summer, the terrace is oriented to the west and you can catch the sunset, but during the winter or a stormy summer day you will certainly prefer to enjoy the indoor atmosphere. I must confess I spend more time there for lunches than for shows.