Yesterday I finally was able to do the critical experiment, testing the competence phenotype of cells with both genes knocked out. It's normal!
And here's the data:
The asterisk on the HI0659 column indicates that this is a 'less than' data point, since there were no transformant colonies on any of the plates.
This result confirms that HI0660 does something that COMPLETELY prevents transformation, and that HI0659's job is to prevent HI0660 from doing whatever it does.