AC3 audio is FAR too soft even after changing Master Gain

I changed the Master Gain in the AC3Filter settings from the Control Panel, but here no results. Also, if it's any relation, the Apply button for the AC3Filter settings always stays gray even if I change things. I encode my dvd's with AutoGK which usually sounds fine, but when I try to shrink a movie too much (like over 2 hours on one CD), I guess it switches from MP3 to AC3 audio, and the volume is terribly low. Another possibility is that perhaps the dvd's I encode that are originally multichannel ones, while the ones that sound fine were 2-channel, but I haven't verified this. Does any one have any ideas? And is there any way to force 2-channel MP3 output since that's all I need.

What you need is some kind of dynamic compress. There's a dynamic compression plugin with foobar2000.

Could you please explain what you mean by "dynamic process" and foobar. Does that go through and reencode the audio and at the same time normalize/amplify it or what? How do I get the stuff?