Rams like very warm and soft water - temps 84. I don't think they would do well with the rainbow's needs - moderate hardness, cooler temps - 78. Plus, with all that swimming around, the rams might choose to stay hidden away, thus not being a really good centerpiece fish. I'd stick to the angels for a centerpiece.
However, you could go to 2-3 Bolivian rams. They like things a little cooler than their blue cousins, perhaps keep the tank at 80 which would also be great for the angels. Also, bolivians don't mind a little harder water than the blues, so they might work with the rainbows.
Cathy