Is it possible to switch from one activity to another without powering off?

Yes, I do it all the time. I have my satellite & digital pvr audio going to my receiver, and the component video outputs going into VIDEO 5 & 6, respectively, into my tv. If I'm watching the satellite & press the "watch pvr" activity button, the receiver automatically changes its input to the pvr audio & the tv switches its video input to pvr.