I've heard that the PAL DVDs are supposed to be unaltered too, but I've only read it on Wikipedia, so...
I have seasons 3 and 4, and I also noticed something else. I only checked episode 301, so I don't know if they're all like this, but it had this really weird sounding echo effect, like they held a microphone up to a TV to record it. I don't know if it had anything to do with the fake surround sound or what (was listening to it in stereo).
Hopefully if it is just a fake surround thing, there's a way to fix it with hardware or software, as opposed to reencoding the whole thing.