There still seems to be a little bit of confusion here... The HDMI does still send an audio signal to the receiver... The problem is, the receiver is not doing anything with the signal coming into it other than passing it right on out another port... Meaning it is not 'grabbing' the audio off of the cable... It is just feeding it on through... which requires for audio to be sent to the receiver in another way...
This is true for HDMI pass through receivers. To get the audio from the HDMI to the receiver you either have to run separate audio from the device feeding the HDMI or run an audio link back to the receiver from the TV.
If the receiver has HDMI repeater capabilities, it can directly access the audio on the HDMI for direct processing in the receiver while sending the video on to the TV. (The Onkyo 606 which is recommended earlier in this thread does have repeater capabilites.)