I don't have experience with this particular config, but some other observations I've noted over the years:
Your USB and/or network stacks need to be disabled for WHDLoad. The hardware interrupts they generate cause a conflict. You can set them to automatically turn off (and restart when quitting WHDLoad) in S:WHDLoad.prefs
With CyberGraphX, there's a setting to always enable 56KHz audio modes. I've found that this causes *huge* problems with native screens, especially with WHDLoad. If P96 has something similar, try disabling it.
