ports-mgmt/portdowngrade. I found that b27 has been the last stable Java in my Serviio media center. On b28, Java doesn't close files and eventually pegs the kern.maxfilesperprocsysctl(). On b29, Java causes kernel panics on 9.2-RELEASE. Portdowngrade is your friend in situations like this.
Where are you getting the revision number from? portdowngrade java/openjdk6 shows the highest revision is 339177. The one I am using for Serviio is an earlier one. portdowngrade java/openjdk6 329761 fetched the revision that works well for Serviio.