I've managed to get 5.1 working in Media Center for DVD's (DTS and Dolby Digital) but for AVI's it either upscales 2 channel to 5.1 Dolby Digital, or 5.1 down to 2 channel. I want it the signal to be unprocessed. For PCM leave unprocessed (my OGG encodes were being detected as 5.1 Dolby Digital audio!) A 5.1 DD AVI is ok in Media Player (5.1 DD singal on amp) but in Media Center it shows 2 Channel AC-3. BAH! What settings in AC-3 Filter (Main, Mixer and System) do I need? And under FFDSHOW? Codecs -SPDIF or LIBA52/LIBDTS. ah I think I got it, in AC-3 filter, SPDIF for DD/DTS passthrough, deselect PCM, DD & DTS in "use AC-3 filter for.." FFDSHOW SPDIF DD and DTS.