New Surround System: Question about Settings

[Old Geezer]

Here's the situation; I recently bought a surround system (Polk speakers and sub-woofer with Onkyo 606 receiver). DirecTv Hi-Def sat receiver and Blu-ray player hooked up to 606 with HDMI cables and HDMI cable out from 606 to TV. Sounds great when I play a Blu-ray. This is the strange part. My Directv sat receiver sends me both hi-def and standard digital signals for the local channels. (I have 2 channel 4's, 5's, ect.) When I play the hi-def channel the picture is great but the sound is quiet and comes only from the front speakers. Sounds thin and weak. Front panel reads HDMI with three small boxes to the left side. When I switch to the non hi-def channel the sound comes from all speakers. Sound is much louder and fuller. Front panel reads PCM and HDMI DSP. Is this something others have noticed? Is there a setting I've messed up. It just doesn't seem right but the sound is so much better on the non hi-def channels that I almost stopped watching the hi-def channels.