If you compress or gzip the unloaded file, it will easily fit on a standard dvd, if you don't want to do that use a dual layer dvd (9.1gb). Download a copy of Microlite Edge,
Home of Microlite BackupEDGE / RecoverEDGE, or install "cdrecord" (skunkware) and backup the unloaded file. You should be able to read the dvd on the HP machine, and use tar (in the case of Edge) to extract the data. (I have never used an HP-UX machine.)
I have customers that backup and verify 10gb of disk to dvd in less than an hour.
Samba, or Visionfs is also available for SCO, assuming you have enterprise and not host, and I assume that Samba is available for HP.