I've looking into this option as well:
SBZ (OEM) > SPDIF (2ch virtualised 3D) > external DAC/AMP (Maverick Audio TubeMagic DAC or an Audio-GD 15.32 etc - any that accept SPDIF in) > Stereo headphones.
One thing though - and I'd appreciate some help - in the new SBZ control panel when outputting via SPDIF, can you select 'Headphones' as opposed to Speakers in the Creative CP? I know that you've got to select Stereo Mix as well.
Creative Control Panel (Click to show)
If you can only use Speakers (in stereo - pretending they are headphones), then this is brick wall. Although the X-Fi's could output stereo CMSS-3D Headphone and work well via SPDIF, I worry that new SBZ Studio would mess up the HRTF for gaming* if you are forced to use the speaker option.
*This is when using the lineouts to an external amp, not using headphone out. (and sorry Ethan if you're reading this! - just want to get it right)
@EDIT* DJI - you beat me to it :) Also - the image you posted when it says "select speaker in playback device".. doesn't that refer to the default device in windows sound control panel, where many would make the mistake of selecting the SPDIF out, not "Speakers"?
Edited by SaLX - 10/16/13 at 1:23pm