Which version of AC3 filter? Why I'm asking?
Because several versions 1.xx appear to have some difficulties with SPDIF.
Personally I'm still using stable version 0.70b (which only supports AC3 as opposed to the newer alpha (
and the very recent beta) versions which also support PCM-sound)
Since just a week or so there is a new and apparently quite stable beta version 1.10b, but I've not installed it, as the 0.70b version I'm using, fully covers my needs.
Read the information at
http://ac3filter.net/
and
http://ac3filter.net/forum/viewtopic.php?t=175