A few years I was also searching for a marriage in Louisville. Through message boards I was able to learn that The Filson Historical Society has marriage records. Through another person on the board I was able to contact someone who does research at the Filson. It was expensive but I was able to get a copy of the Marriage Certificate. The Marriage Certificate listed bride, groom, county, witnesses and signed by - which turned out to be the priest that married them. I searched his name and was able to narrow down the name of the church.
Since the church was closed I contacted the Cathedral. They found the marriage record for me.
You can contact me through member connect under Gem5955.