Congratulations. The Casablanca is a nice piece of equipment. Do you have the user's manual? It describes the connections very well.
It looks like you have the standard balanced DAC. A balanced output has two phases but a RCA single ended output has only one. Usually, when you convert a balanced output to a RCA you will only use the positive phase but Theta provides you with both so you have a choice. You can just use the one marked with + and ignore the other.
I don't know what sub you have and what you are trying to do. Normally, I would by-pass the sub's crossover (if your sub has that feature), connect the sub input to the sub output of the Casablanca, and just use the crossover from the Casablanca. The Casablance's crossover is very flexible. Don't waste it.
It looks like you have the standard balanced DAC. A balanced output has two phases but a RCA single ended output has only one. Usually, when you convert a balanced output to a RCA you will only use the positive phase but Theta provides you with both so you have a choice. You can just use the one marked with + and ignore the other.
I don't know what sub you have and what you are trying to do. Normally, I would by-pass the sub's crossover (if your sub has that feature), connect the sub input to the sub output of the Casablanca, and just use the crossover from the Casablanca. The Casablance's crossover is very flexible. Don't waste it.