Assymetric recording isn't unusual - a lot of instruments produce waveforms like this naturally, and so does the human voice. The only interesting thing is that almost invariably (because of the way waves travel through air) the assymetry is generally the other way around - the larger peaks are positive.
One other thing that can cause non-symmetrical waveforms is a DC offset - but looking at the end of your file, there doesn't appear to be anything significant happening in that direction. So the only thing I think you have to do is to invert the signals. It's possible that some previous processing may have caused this to happen, obviously - but unless it happens with every single recording you make, there really isn't anything else to be done.
To be quite honest, I am very impressed. I did not think anyone would reply so soon, let alone reply at all to my question. You have given me quite a bit of info that will allow me to do plenty of trial and error to see, just for the heck of it, if I can't get a more even waveform. Thanks! It's great to learn new things! Since most of what I do, at least up until now, is simply remaster music, I haven't really had to deal with this phonomenon, but I suppose branching out will provide plenty of challenges along the way. Thanks again!