Two points:

(1) As a long-time [stereo listener historically] "biamper" my connections have been [since runs have always been short] unbalanced.
If I were going to biamp now that I have surround [990 and 755 and I'm not] I would probably simply use an RCA-RCA-RCA "Y" adaptor Still, the idea of using the balanced as well is interesting and I wonder if you can use them both at same time.

Question about this: Is there a difference in level at bal and unbal connections.

(2) Just a point of info: The balanced connectors onthe 990 are XLR's. BNC connectors are often found on video [most often pro] eqpt.