lastdeja>
The SPDIF passthrough option in 1.01a RC5 is in 'System' tab it works well (I think that indeed there was some messy version as BSPeter said, I mean that release from 05/2004 that was ok). You may try to get the latest version 1.02 test3 from
http://www.free-codecs.com/download/AC3_Filter.htm and check if it works.
Anyway, I have heard some people having troubles with Audigy2 and mostly the new drivers from Creative did help them.