Which settings/codecs for streaming movies from PC to Home Cinema Set?

[Spiritos]

I recently bought a Sony HT-SS1300 HCS (with some help from the people here) and I have some questions:

1) I predominantly play movies on my PC which is connected with HDMI to the HCS and then unto my TV. I use Media Player Home Cinema and I was wondering what settings and codecs I'd need to stream 5.1/DTS/Dolby etc.

I know little about all formats and such -so while I hear audio through my speakers- I'm unsure if I am getting the BEST possible sound (depending on settings and codecs) so which settings and codec should I use?

2) The HCS is capable of playing True HD but does not encode so which setting/codec do I need on my PC to be able to hear True HD?

3) Since I am new to 5.1 setup I don't really know how to judge the sound. What I notice is that when I play a movie (AC3/DTS/5.1/Pro Logic) the dialogues are pretty soft and then suddenly car chases and such give an unpleasant boost to the volume.

I have set compression to max on my HCS to lessen the dynamic range and lowered the output of the sub but still.. Is this broad shift in dynamics usual or has this to do with codecs/settings?

 

[Spiritos]

Appearantly reinstalling Realtek drivers was one of the culprits.