The Audio drum loops are wav files, so it is impossible to edit or replace one drum just as it is impossible to edit an mp3 file.

I do not see this as a problem. If you were playing with a live drummer you couldn't realy say to him..."I don't like your snare, do you have another one in the van?" And I don't know many bands that would ask their drummer to "sit this one out" because they have a midi drum module that sounds beter.

I have a theory that if certain drum parts are seem unbalanced its often down to the PA as some favour certain frequencies and many modern systems lack mid range almost completey.