Ok here is my take on this...
In short:
The only available "pass through" setting for the extigy applies ONLY to the software SPDIF-in (the one coming e.g. from a software dvd player like powerdvd...)
The physical optical-in is unaffected by this option and will regardless of its setting be decoded by the extigy (extigy's DOLBY light goes on)
If your receiver has multi channel in (my low end sony does have it), you can get dolby digital 5.1 from you console without having to switch optical cables around. Just let the extigy do the decoding and hook up the front/rear/center channels to the receiver's multi channel in.
I am pretty sure there is no other way around this. Initially the Extigy didn't even have the pass through feature for the software spdif-in. It needed a firmware upgrade to change this.
Since there are no newer drivers available... there is no chance.
My above assumption for two kinds of "pass through" was not so off: see quote from creatives knowledge base below ("by pass" option set in AUDIO HQ and "pass through" option). Essentially the physical optical-in can only be "by-passed" to the optical out on Audigy cards and livedrives.
For me the solution is fine now: I don;t have to change any cables or configuration settings: I can get DD5.1 from my console on all my speakers (Extigy decodes and it's dolby light goes on) or play a DVD on my laptop and get DD5.1 again and the sony receiver decodes (shows the blue light).
Again all I have to change is switching the receiver between multi channel in and optical in.
I would have preferred to have the receiver do the decoding also for the console. I also tried to match the output frequency of the PCM signal to the console's: (using PCM 48 in the control panel instead of PCM96) . I was hoping the by-pass would work then, but no success.
So as it is right now, with the multi channel hookup between extigy and receiver you get your console's 5.1 but if the PC makes a noise (e.g. line-in or wave) it gets mixed together.
QUOTE FROM CREATIVE KNOWLEDGE BASE:
Solution ID # 8921
What is S/PDIF Bypass and S/PDIF Pass through?
Keywords SPDIF, S/PDIF, bypass, passthrough, digital,pass-thru
Applies to Sound Blaster Live! series, Sound Blaster Live! 5.1 Series, Sound Blaster Audigy series, Sound Blaster Audigy 2 series, Live Drive Series, Audigy Drive, Audigy 2 Drive, Digital I/O Series, Sound Blaster Extigy
Our Advice
What is SPDIF?
To view the Knowledgebase article on What is SPDIF, click here.
What is SPDIF Bypass?
The SPDIF Bypass feature allows users to route digital signals from SPDIF Input to SPDIF Out without going to the effects processor. It allows users to share SPDIF Ouput path through the Digital I/O Module from the card or another SPDIF output device (for example, DTT3500),without the hassle of plugging in and removing the connection to the single RCA input from either of the two devices.
To enable the SPDIF Bypass for the Sound Blaster Audigy/Audigy 2, go to Start, Settings, Control Panel and click on Audio HQ. In Audio HQ, click on the tab for Device Controls, then click on Digital Input. Within the SPDIF box, click on the down arrow on the right side to view the SPDIF options, one of them is SPDIF Bypass.
To enable SPDIF Bypass for the Sound Blaster Live!/Live! 5.1 series, go to Start, Settings, Control Panel and click on Audio HQ. In Audio HQ, click on the tab for Device Controls, then click on Digital I/O. Check the Enable box
Note: the SPDIF Bypass is only available if there is an Optical Digital I/O card or a Live!DriveII, Live!DriveIR, AudigyDrive, Audigy2Drive or the external Digital I/O Module are installed.
What is SPDIF Pass through?
The SPDIF Pass through allows the Sound Blaster card (Sound Blaster Live! 5.1 or later cards) or a software DVD Player to pass the SPDIF signals to an external decoder. It may also be labeled as SPDIF Pass-Thru or AC-3 Pass-Thru.
To enable SPDIF Pass through on the Sound Blaster Extigy, click here.