I don't know why but the 5.1 tracks on blu seem to sound alot "bigger" than the ones on SD-DVD.
If you're using a PS3 as your Blu-Ray player (like many people), then you'll never get the DTS HD-MA or Dolby TrueHD display to light up on your receiver. The Ps3 is incapable of passing the encoded audio to your receiver.
It'll still sound just as good, but your receiver won't show the encode type.
I just love it when my Denon Lights up and says DTS HDMA!!!!!