Pc to a/v receiver only getting 2 channel sound

wasn't sure if i should post this in the video card section or home audio section so i posted in both. ok so i installed an HIS 5770 video card with hdmi output that puts out up to 7.1 sound. i also just bought a sony STR-DH800 receiver. so here's my set-up, i have a dvi connected from my card to my 19" lcd monitor and that's my primary monitor. i have an hdmi cord going from my card to the receiver and have that be my 2nd monitor(receiver is connected to my 56" samsung 1080p dlp). my tv is working great as a 2nd monitor. the display on the receiver says "linear pcm" which should be correct. i'm getting sound from my receiver, but only through the two fronts. so i went into my sound manager in my control panel and ati hdmi output is checked as the sound device. i went into configuration and stereo was selected so i switched it to 5.1, but i'm still only getting 2 channels. i go back into configuration and "test speakers" and the receiver display shows that it's doing something but NONE of the speakers make any noise, but the front two work when i play a file. what the hell is the problem?