I am not impressed by "Auto Unpack", it does not handle the unpacking correctly for some files. In fact, "Auto Unpack" shows error messages while other programs can handle the same files. There is another automatic unpacking, which may not be much better than "Auto Unpack". If you want to give it a try, look for Par-N-Rar at
http://www.milow.net/site/projects/parnrar.html
While I have not seen a good program for automatic postprocessing, the manual postprocessing with QuickPar
http://www.quickpar.org.uk/ seems to be quite good. Manual postprocessing means that one has to load a par file, the rest can be done automatically as well.