Well, you were quite light on the details, but I have a similar setup that I was able to get working.
I assume you installed the 18.9 kernel via Redhat RPM for both source and binary. Assuming that went well, try to rpmbuild --rebuild the nforce driver set.
It dies with Error 2 or something like that. From there, you have to do the following:
# cd /usr/src/redhat/BUILD/nforce/nvnet
# make clean
# make install
Assuming all goes well, reboot. Kudzu, if you haven't been smart enough to disable it will appear asking you to configure the new card. Assuming you had the card configured correctly prior to the upgrade, you can skip this step and it should just work.
Don't bother trying to get nvaudio to compile. Nothing has worked for me.