I don't know Soundbooth but any audio program worth using should be able to import an OMF which FCP can export. An alternative is to export your project as an XML and import that into CS5 Premiere Pro which is alleged to import FCP XMLs. From there, there should be an export path to Soundboot. It may even import a FCP XML as well.
Talk to your sound post person. They should know what they want and what there system can import.