General what you shoul do for multisessios
1You should ask for a CDInfo to see if the disc is empty or not (handle OnDoneCDInfo).
2If not empty, you should import a track using ImportIsoTrack (handle OnDoneImport or OnDoneImport2).
3You should now create a NeroISOTrack object and add to it whatever folder hierarchy you want and optionally add the imported folder structure.
4Finally, you should call BurnIsoAudioCD.
I have code only in c# but i think you sould read this thread