Here are my thoughts; they may not be correct:
I'm not familiar with Toast or with enhanced CDs, but I gather that enhanced CDs combine audio tracks and data tracks, and can be played in standard audio devices. If so then their file structure is presumably not Mac-specific.
The documentation for AutoOpen, however, states:
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How it Works:
An HFS+ volume has a header which stores, among other things, an identifier for the directory that should open when the volume is mounted. AutoOpen is a simple GUI method to set that identifier.
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So it looks as if AutoOpen works on HFS+ (Mac) volumes only, such as the disk images that can be created and burned using Disk Utility.
I don't know if there is a Toast forum; if so you might ask there about whether one can auto-open an enhanced CD.