I just thumbed through the Creative support knowledgebase and found
this
If your receiver has a Dolby Digital SPDIF-In, connect it to the Digital Out jack on the sound card with a 3.5mm (mono or stereo) to RCA adaptor.
Note: DVD-Audio cannot be played back via digital speakers.
Discrete Analog Inputs
If your receiver has discrete Line-In jacks for Front Right, Front Left, Rear Right, Rear Left, Center, and Subwoofer:
Connect Front Right and Front Left to the Line-Out 1 on the sound card with a 3.5mm (stereo) to RCA "Y" adaptor cable
Connect Rear Right and Rear Left to the Line-Out 2 jack with another 3.5mm (stereo) to RCA "Y" adaptor cable
connect the Center/Subwoofer In to the Line-Out 3 on the Sound Blaster Audigy 2 card, with a 3rd 3.5mm (4-pole or stereo) to RCA "Y" adaptor cable.
Connect the white RCA plug to the Center input and Red RCA plug to the Subwoofer input on the receiver.