I never head much luck with AC3Filter, FFDshow, etc. etc.
What you need is "bit perfect" playback and pass thru. That means absolutely no modification of the sound by the driver, windows, etc.
looking for an ASIO driver is one way around the "kmixer" problem where windows mixes sound from applications with sounds from the OS.
You could google for "bit perfect" and winamp. If I recall, there is a spam plugin for winamp to SPDIF that works.
http://otachan.com/see this thread:
http://forums.winamp.com/showthread.php?threadid=254383Having said all that, if you are going to do stereo to 5.1 conversion you need a way monitor 5.1 channels BEFORE they are encoded to DTS, or be able to encode to DTS on the fly. Unfortunately, unless your HT accepts spam inputs (and your current sound card has 6 spam outputs) these solutions all have some cost.
There is a ~$35 sound card that might work. I haven't tested it but have tested it's more expensive big brother:
Untested but spam:
http://usa.asus.com/product.aspx?P_ID=w ... templete=2Same technology (DTS encoding on the fly) tested:
http://usa.asus.com/product.aspx?P_ID=S ... templete=2Also if you have 5.1 spam out now, but no spam ins on your HT there is an external box that does DTS encoding on the fly. It's no longer made but you can still find them on ebay, etc. Creative dts-610:
http://us.store.creative.com/Home-Theat ... 651ZEM.htm