That formats use any install package inside...
.pax.gz: is a standard gzipped .pax file.
.pax: "The pax utility will read, write, and list the members of an archive file, and will copy directory hierarchies. These operations are independent of the specific archive format, and support a wide variety of different archive formats. A list of supported archive formats can be found under the description of the -x option." it's similar to .cpio.