So I booted into the cisco firepower console using a asasfr-5500x-boot-6.4.0-1.img and then tried installing the package using asasfr-sys-6.4.0-102.pkg. When I tried using my ftp server to transfer the file and install it I got an error saying:
Package header failed verification - 'Header magic number mismatch'
Please verify that the package is not corrupted. I tried looking up the Header magic number mismatch message and got only one return about someone using a .img instead of .pkg. I'm really not sure what the issue is as the management interface can ping the ftp server and the .img worked fine.