But if the unit had 2 drives to begin with, how do you plug both the old drives *and* the new drives in at the same time?

Do you do them one at a time?

If I had to guess, if there's 2 full drives, and the upgrade path is to 2 bigger drives..

Remove Drive B,
Plug in empty Drive C
Copy Drive A to C
Remove Drive A
Plug in empty Drive D
Remove Drive C
Plug in Drive B
Copy Drive B to Drive D
Remove Drive B
Plug in Drive C

will this work? Or is there easier ways?

Can the contents be backed up onto the computer, both drives removed, new drives put in, and resynced?

Calvin