Windows only allowing 2 channels to RCA2906 Receiver

I know there are several similar problems about not getting 5.1 sound out of a computer, but none seemed to help me figure out my problem. I have an ASUS Desktop PC CM6850 with an nVidia GeForce GT 530 graphics card. I have the computer connected to my RCA 2906 5.1 surround sound receiver input via HDMI cable, and the receiver HDMI out connected to my LCD TV. In my playback devices, I am only seeing my TV (even though it's not directly connected), which only has the option of configuring the sound to 2 channels. I've tried installing drivers from nVidia, rebooting, plugging into different HDMI inputs on the receiver, and and flipping through the surround settings on my receiver.

For the life of me, I can't get my computer to recognize the fact that the receiver is connected to it, and not a tv with stereo speakers. I've tried contacting RCA, but they haven't responded yet. I don't know if it's my computer or the receiver, but I've gotten 5.1 sound through the receiver from a different source, so I know it's not the speakers. If anyone knows why this is happening, that would be great. I would hate to think I've wasted my money on something that should have easily worked.

I don't think that's true. In playback devices, my computer has it labeled as an LG LCD TV, so it clearly knows what's plugged into it on the other side of the receiver, or it wouldn't know the brand. There wouldn't be anything listed as plugged in at all if there was nothing on the other end of the cord.

Is there a way to force the computer to put out 6 channels regardless of what's plugged into it?

It is supposed to be capable of both 5.1 or 7.1 audio, and only has HDMI, DVI, and VGA connections for the graphics card. The computer does have an additional HDMI port but it doesn't display anything when I connect to it. There is also a digital optical out that I was using to play sound through to the receiver before using the HDMI, but I was never able to get 5.1 through that either, which is why I'm trying the new cord. Since there was no option (not even grayed out) to select more channels with either connection, I assumed it was a computer issue.

GeForce GT 530 (OEM) - Specifications - GeForce

The specs for the computer do say "8 channel high definition audio"

Asus - Essentio Desktop / Intel® Core™ i7 Processor / 8GB Memory / 1TB Hard Drive - CM6850-07

You have the drivers for the video card installed,

NVIDIA DRIVERS 280.26 WHQL

which also contains the audio driver for the card's built in HDMI audio.