They all get along. Pacu very calm....same as my flowerhorns. My flowerhorns were very aggressive, especially the SRS when he was in his own tank, but in harmony in the community. The rainbow shark is one of the oldest (my sons) and has survived from the beginning. Aro has been raised in a community since he was 6 inches when I first got him....now 24+ inches.
Here is a vid of the harmony.
http://www.youtube.com/watch?v=hF4XbxNOgTE
Hoping to upgrade my community tank to a 10 foot tank and also planning to add a RTC in the near future!!!