In order to get stereo out the answer to where you connect the ANALOG STEREO cables is to the corresponding analog stereo input jacks. So...if running a toslink or coax assigned to a specific input you should also connect your RCA's. This will allow the audio to be output thru zone 2.
Zone 2 does not "pick up" digital...only analog. So any analog signal which is fed to 990s analog input will appear on zone 2 output. BTW this is not true for record out. Video 1 does not...don't know why
So remember that if you are using a digital signal to feed a given 990 input simply also send an analog stereo signal to it.
Now, re: the Russound. I've never seen or played with one, but if it has an extra "line-level input" (an example would be labeled such as "aux" or "tape" or "tuner" or anything other than "phono" you can send the zone 2 output to it and control it with the little zone 2 remote.
HTH. let us know