You can use program "AC3Filter" which passthrough the sound via SPDIF. Its working for WMP including Media Center. Havent try for HDMI connection, but I doubt it, as didnt found any option.

Before, my source is in FLAC, but now converted to WMA due to FLAC have a IDtag and album art compatibility with WMP (even with WMPTSE plugin). But with WMA, I cannot get the 5 channel signal to be played properly. Anybody get to play DTS song contained in WMA?

if you connect sound card digital output / spdif to receiver, you get dts sound, with dts indication at receiver as sound is decode by receiver

if you connect sound card 3.5mm jack to receiver rca for all 5 channel, you still get the dts sound, but no indication at receiver as sound decode by soundcard

hope this is the answer

If on Vista, you have to disable TMM (Transient Multi-Monitor Manager) at the Task Scheduler. Then the last setting on both display shall maintain even second display is off. But if you restart the PC, the setting of non connecting display still will be gone. I've yet to found the setting auto detect second monitor with preference setting. I'd like to know also.