It’s hard to tell, what the problem is, not having the Saturn Emulator and its sources (and the time to analyze it). I guess, it sends some unusual SCSI codes that WinCDEmu fails to handle. Or this can be related to some copy protection mechanisms. Basically, WinCDEmu is a tool for mounting CD/DVD images with PC data, so, strictly speaking, using it with a specific Sega emulator is out of its main functionality. If you have free time (and some basic Windows Kernel knowledge), I can suggest what to look at in the debugger to determine, what does the Saturn Emulator want.