I don't think there is a one, easy method to do all this.
If you have DVD-Audio, try googling DVDAExplorer. It can extract the audio stuff very quickly and put them into multichannel wave files - with no sampling rate changes and stuff. Some audio processing programs, like Adobe Audition, will open each channel as separate track. Sound Forge does it better, because it supports surround audio. No idea about Audacity.
If you want to extract a DVD-Video's audio... it's quite problematic, unless... you can use DVD Audio Extractor. It's commercial software, but the trial version should work with no limits for 30 days.
As for free software, I think I'd use MeGUI (http://sourceforge.net/projects/megui/
). It's a video conversion utility, a rather complex one too
First, copy the DVD contents to your hard drive. Might need to use some ripping software if the disc is copy protected.
Then, in MeGUI, go to Tools, then File Indexer and pick the first largest vob file - that should be the main video track. The window should show you the audio tracks detected. Make sure the option to demux audio is selected. Click queue and go to the main window's queue tab and click start. This will give you the ac3 or dts file in the video_ts folder.
Now, depending on whether your audio editor supports it, open the files directly or convert them to wave files. To convert ac3, any of these should do it: http://www.videohelp.com/tools?convert=AC3%20to%20WAV
As for dts, I have no idea.
To use the two front channels for dynamic range analysis, it depends on the audio editor you use. In Adobe Audition, each channel is a separate track. It should be easy to sort them all in the multitrack view - just leave the two front left and front right channels there and downmix it. In Sound Forge, just select the front channels and copy them to a new stereo wave file. Again, no idea about Audacity
I hope anything I wrote helps. If there are easier (freeware!) methods, I would also be happy to learn about them
edit -- edited the post quite a lot!