There are two ways to do this, analog and digital.
You can get a digital coaxial cable and conenct the Audigy2 to the digital coaxial input of the receiver. This ensures that it will be the [probably] superior DAC chip of the receiver that does the job of converting digital data to analog audio you can hear. But, there are caveats: 1. Creative shut off the digital output if the card is playing DRM protected material (e.g. DVD-Audio and copy protected multimedia files) and 2. As games don't have Dolby Digital encoded sounds you won't be able to do 5.1 gaming like this.
Connecting the analog outputs of the card to analog inputs on the receiver may result in a bit lower quality of sound (because it's the DAC on Audigy2 that's doing the conversion, although you may want to know that it's no slouch either) but it gives you everything.
Now, you can do it both ways too. If cable clutter doesn't bother you, you can use two of your receiver inputs, one for analog and one for digital input from the sound card. Switch to analog when playing games or playing back copy protected DRM media like DVD-Audio and for everything else, use the source with digital input.