Originally posted by: BountyHunter

what was the bitrate for the 04 DVDs?

Furthermore, would the 2.0 decoded into pro-logic sound nearly as good as the 6-track (70mm) audio?

Bitrate for the 2.0 tracks on the 2004 DVDs was 192kbps, which is pretty much the standard for 2.0 tracks. Some companies have used 384 kbps, but not many.

In answer to your second question, a 2.0 track, by nature of its design, is not going to sound as good as 6-track 70mm. It may come close to sounding like Dolby Stereo in a theatre (4 track surround matrixed into two tracks), but it will lack the "baby boom" elements of a 6-track 70mm track. For that, you would need a 4.1 DD track.

Keep in mind that Dolby Digital (AC-3) is a lossy compession system, so something of the original tracks will inevitably be lost. The only way to come close to the original theatrical sound experience is to use a lossless audio codec, like Dolby TrueHD, which uses MLP (Meridian Lossless Processing) for compression.