A sound card plugged into the motherboard's PCI-E slot will have access to more power, like for driving headphones.
But if you prefer to go with a Creative Labs USB sound card (AE-5 or other), go for it, as it seems to have more of what your looking for anyway.
The newer AE-5 plus comes with DDL (Dolby Digital Live) and DTS-Connect software, which can encode (compress) up to 6 audio channels (5.1) of digital audio, allowing that audio to pass thru S/PDIF (optical/coaxial).
The compressed audio is maxed out at 24-bit/48K, which is still very practical for most uses, but the device receiving that encoded audio would also need DDL or DTS-Connect to decode the audio back to PCM.
Otherwise S/PDIF optical/coaxial will only pass 2-channels of un-compressed (PCM) digital audio, but that audio can be 24-bit/96K or 24-bit/192K.
If you connected a optical DAC/amp, for headphone use, you would only need the 2-channel to pass thru S/PDIF anyway.
Thanks @PurpleAngel. With the g6 if I am playing Hunt which outputs binaural do I set windows to 2.0 and then windows to 7.1 when I want to use sbx? Or just leave windows on 7.1 and turn sbx off when playing hunt?