550 and Onkyo 606

[GlobalMischa]

I've got a setup in my livingroom:

Onkyo 606, HDMI output to the TV
BD-S505, HDMI to the receiver.

It's maybe a total newbie remark/question, but at every movie I press on the "DISPLAY" button on my BR it prompts "Dolby Digtal 3/2.1".

Now, is that 'normal' or is there some setting I didn't set? I've tried everything, but I'm not getting any Dolby Digital 5.1 (or something like that). Or doesn't the DISPLAY button have to say something like 5.1?

Thanks in advance for your time.