So you're just talking about transferring the domain accounts. If you have root access (or just ssh access) on the plesk server you should be able to transfer them using cPanel's account transfer feature. If you are root on the new server, you will see this option in WHM, if not, your host should be able to help you with the account transfer.
3RROR.COM Web Hosting
Hosting to Dedicated Servers Providing Personal and Small Business Website Hosting since 2003