I don't think that will make any difference, although it is a good idea.
Your network is only 100Mb?
6TB = 6000GB = 6000000MB = 48000000Mb (Megabits), transferred at 100Mb/s = 480000 seconds = 8000 minutes = 133 hours and 20 minutes. And that's assuming full utilization of the network capacity, which never really happens.
If you upgrade your network to GigE, you can cut that to 13 hours and something (again with ideal assumptions).
If you follow the strategy I suggested earlier about breaking up your 6TB into many smaller segments for backup (by specifying directories and/or exclusions in Amanda's disklist file), so that you aren't trying to do the whole thing as a full backup all at once, that can make a big difference. For example, if that 6TB were home directories for an organization, you could specify each individual home directory in the disklist, or group them alphabetically.
Did you configure this installation of Amanda? Or has it just been handed to you, and you have to figure it out? If so, you might need to spend some time just reading up on Amanda --
http://wiki.zmanda.com/index.php/Main_Page. Make sure you understand Amanda's planning strategy --
http://wiki.zmanda.com/index.php/Backup_Levels.
