I think I mentioned it in your other thread, but I've had redbreast kill a rockbass. The problem isn't the non-territorial fish, it is the territorial fish killing the former. Crappie will adapt to tank life better at a young age, but if you don't want your redbreast to kill the crappie, you've got to get a fish that is larger than your redbreast.
What size is your tank? Depending on this, you may just be able to get more sunnies and crowd the hell out of them. I've already told you my various experiences on redbreast in your other thread, so I won't comment further.