Now help me understand the Audio

[Arioch5]

I think I've got my video looking good, it's time for me to better understand how these audio decoders work.

I downloaded the Nvidia decoder for MPEG-2 content and the video looks good I'll probably stick with this. The one thing I didn't like about it is my audio is all over the place. I *think* currently the SD content sends the audio through AC3Filter, and the HD content is getting picked up by the Nvidia decoder. When I watch SD content the Audio can be easily adjusted up or down in AC3filter settings. When I'm watching HD content the Nvidia decoder seems to only let me adjust the volume down (can't go above 0db) which is a problem because the HD content is much quieter than SD content.

My question here is multi-part.
First, lets talk about how I can get SD/HD/DVD/Xvid to all be around the same volume level. Keep in mind I also use this computer for gaming/etc. I'd like the volume in my games to be around the same as everything else.

Second, how does this all change if I decide to try and support 5.1 output from the computer. I will end up doing this eventually I know. I would of course have to buy an audio-card, and my receiver's only optical input is in use, but I could use the SPDIF I think i still have one of those available. Would this solve some of my issues? I'm curious if windows will send all audio out (SD/HD/DVD/Xvid/Games/etc). If so, does that help with the issue I'm currently having?

Some of the basics of my setup are in my signature and I know I've looked at this stuff a while back but I never did understand *what* was decoding my audio and why they levels are all different. I know i have ffdshow/AC3fileter/ and as of last night an Nvidia decoder now installed. I think I'm going to keep the Nvidia decoder b/c the video on my test last night looked good (though a bit quiet).