I would probably not recommend using XPression Connect for this.
Tagboard is supported using the Datalinq RSS data source in XPression version 8.0 and above. Tagboard's v1.0 API can be set to RSS and is formatted in way XPression can read, including downloading of http images (avatars, attachments, etc).
You can reach out to Tagboard for help setting up their RSS output.
#XPression