Please note that, in order to preserve the native display properly, the second card MUST NOT be in the display chain as otherwise P96 leaves screen switching to graphics, which attempts to switch the native graphics away from the amiga native chipset to the card, and then displays whatever is left in the chipset registers by accident. That is, the DISPLAYCHAIN tooltype of the ZZ9000 monitor driver shall be "NO":
DISPLAYCHAIN=NO
Unfortunately, all but the latest versions of the ZZ9000 driver seem to have had a bug that it always overrided this tooltype and always places the card into the display chain, regardless what the user requested, see also this thread on eab:
http://eab.abime.net/showthread.php?p=1502029
This may be fixed in the latest driver, but we can't test that, as we don't have a ZZ9000.