What are they? I see that the 990 has these. Do you need to have balanced inputs on the amp as well? I just purchased the 7100, perhaps I should have waited for an amp with balanced inputs.

You would be better off just doing the RCA - RCA connections since the amp doesn't have XLR inputs. If your runs are short, you probably won't miss a balanced connection. Opinions on whether balanced are an improvement are as varied as opinions on cable brands.

I personally prefer balanced as my amps have balanced inputs, which is why the 990 is one of the Processors on my list.

I see no reason to second guess your choice of amps. Balanced inputs are borrowed from the recording studio, where they are used to cope with the high levels of background interference that can exist (particularly over longer runs). You do not need balanced inputs on your amp to use the 990, although those of us with unbalanced amps will want to use the unbalanced outputs and simply leave the balanced connections alone. I expect a significant majority of Model 990's will be connected to amps with unbalanced inputs (such as your Model 7100). Some people will use the balanced outputs because they have gear such as EQ's downstream of the processor that use balanced connections or they already own amps that have a balanced topography.