TV + PC Speakers Help

[Mechanicus]

Hello.

A while back, I set up my PC to a monitor/speakers and my TV.
I don't know what the setup was, but both the TV and Speakers could play the same sound at the same time. This meant that I could turn off the PC speakers and watch a DVD through the PC, using the TV's speakers, without having to swap wires or muck about at all.
I was using the on-board sound of the PC, and had no splitters or anything, just 2 cables - 1 for PC, 1 for TV.

However, I recently upgraded my PC, and put a new motherboard in. I also had to format the hard drive because of the amount of hardware I had installed.

Now everything is up and running, I have no idea how I set this up!

I have a feeling that my old motherboard allowed me to choose which socket did what - so when I plugged something into it, it asked me what it was I was plugging in, and I could select from a list.
This new motherboard, which uses Realtek HD onboard sound, doesn't give me that option.

Can someone please give me advice on how to set this up, that won't require me buying any other bits (splitters, additional sound card etc.)?

I tried switching it to quad-speaker surround sound, but it plays the TV speakers as back speakers rather than 4 front speakers.

[Erazerhead]

you might want to post exact specs of your mobo/onboard sound.

There are different HD Audio codes. Besides - if the manual does not give you the way to set outputs for dual stereo operation it can't be done in software, but then a splitter costs perhaps $0.99 so why to bother?