Only one user can be connected to a slingbox at a time. and whatever source the slingbox is connected to will be seen by the local user and by the slingbox user. so if the local user changes the channel, the slingbox user will see the channel changed (and vice versa).
the only way to have a local user watch tv and a slingbox user to watch tv (but a different channel), is to hook the slingbox up to a different source. so if you have a cablebox/dvr in the living room, the wife can watch that and if you have a cablebox/dvr in the bedroom/den, you can hook up the slingbox to that. This will allow the slingbox user to watch television independent of the local user in the other room.
Spouse is a TV hog - Can I get a second cable box or router (or anything) jus for my Sling Player so that I can watch TV in peace?
Ha. Franknitty nailed it... sure. You CAN grab a second cable box and enjoy the blissful peace. Think of the Slingbox as a TV, functionally that's exactly what it is. You want to watch something else in a different room ? Hook another cable box up to a second TV and go for it.
You don't need another router.
One more thing... if you go for the second cable box, keep the IR blaster in mind if you put the new equipment in the same general location. Wouldn't want to accidentally change channels on cable box #1. (I ran into that when faced with the same dilemma as you)