Ive had success with my 40B (knocks on wood)
Right now its got
5 Ember tetras
6 adult False Juliies
1 small julii baby
2-3 really small baby juliis
4-5 adult RCS
3 adult brown emeralds
about 15 or so babies of shrimp ranging from 1/2" to just over 1/4"
Have scene several very small recent litter of shrimp.
Anyhow thats what Ive got. I am fine with the CPDs being the "center piece fish" and to be honest thats kind of how they act. Well them and the juliis if you dont scare them coming up to the tank. I plan on growing some more shrimps so have a couple bushels of java moss mixed in with all the plants. This is also why the baby juliis are making it I think. I did recently bump up the CPDs numbers to 8 as mentioned so this will more then likely impact the populations of babies as they look like they are more "hunters" then ember tetras.