Hello Markus!
1) I can use amfetchdump to get what appears to be a zip file:
# file staff15.zip
staff15.zip: Zip archive data, at least v2.0 to extract
2) The "unzip" command (which has ZIP64 support) does not recognize
this as a proper file:
Amanda dump images have a 32 kB special amanda header in the
beginning, followed by the actual backed-up data. This header
contains, among other things, human-readable information about how to
extract the dump. In order to extract the dump, this 32 kB header
should be discarded from the dumpfile and the remainder fed to the
specific extract tool. On Unix-like systems this is usually done with
dd. I don't have much experience with such things on Windows, but
something similar surely exists.
HTH,
--
Toomas Aas