Rainbows love to eat! They should put a dent in the crappies but you will need to help them in culling the BCP.
Once you have cut down the crappie numbers and are seeing fewer, but bigger fish, I would stock some forage. It might all get eaten so I would recommend large GSH or FHM so you aren't wasting money. The shiners will ( possibly) survive predation and the FHMs are cheap enough that it isn't a big deal.
