1- Use Song Copy Playable to create a duplicte of your recording. You must have enough free space on your hard drive (or partition) for the copy (change your display to show MB remaining instead of the default time remaining - it will help a lot) If you have multiple partitions on your hd, then you can make the copy on any partition that has enough free space.

2- Song Split could be used, if you have a lot of unnecessary track data in the original SONG and only want to copy the two master tracks (L/R track pair). Understand that song split creates new song files of specifically chosen tracks and/or v-tracks along the entire time length of the SONG. It will not let you split a 40 minute song into 2 x 20 minute songs, for instance.

3- As Drachir suggested, song copy will get you where you want to go, but will require editing of both the original and copy, timewise. Be sure to use Track Cut on the song that is to be the 2nd half of the concert, in order to delete the first half of the song file and pull the 2nd half forward so that it begins at Zero on the timeline. This is because the firs cd track will begin at zero, even if there is nothing but blank space until the start of the first actual track data. (I may be wrong, as it's been ages since i did this routine - so be sure to check the manual for details about using CD track markers - very important!)

4- Be sure to understand and use CD markers to makr your individual songs in the concert, or you will end up with a CD of one long track of which you can only fast forward and rewind on a cd player. Also, be sure to mark the end point of the last track of each half of your 2-part concert. If you don't mark the end as you intend it, the 1680 will include any time that goes beyond that intended point onto the last cd track, even if all you have is a few tap markers past the last song.

Hope this helps. I remember how involved this process can be, because i also used to record long concerts on the 1680 and had to learn all these processes.