The compression, while it can affect the volume, isn't solely to blame. A lot of what is thrown away are sounds that are "masked" or covered up by louder sounds, as well as inaudible or unnecessary frequencies. Keep in mind, also, that I am splitting up what is essentially a 2-speaker soundtrack among 5 speakers. I could have cranked up the AC3 volume more, and dropped the PCM/commentary soundtracks to compensate, but I didn't do so at the time. Maybe next time.

DTS tracks aren't necessarily louder, but they often sound "fuller" because more audio information is kept.