Once you have a backup of the VS1680 project on CD-R (you can do this with Roland's VSCDR burner), bring the session into the VS1824CD using the 'CD-R Recover' function (explained on p234 of the VS1824 Owner's Manual). Save the session to the internal hard drive on the VS1824.

Create a new project on the VS1824, then import the tracks from the recovered session into the new song (see p151 of the VS1824CD Owner's Manual for this procedure). Importing the tracks this way allows you to record new material on top of the recovered tracks.

Note: You can open the recovered session on the VS1824 without importing the tracks, and you'll still be able to listen to the tracks, adjust the faders, etc. However, if you attempt to record in this state, a "session locked" error will come up.