You can do an in-place upgrade and migration. No export/import necessary. Make sure you do a cold backup though.
This is not a trivial process, and I recommend doing the database migration by hand--my experience with the GUI migrator was that it had memory leaks and failed in the middle of the migration.
Is 8.1.7.3 the latest for Sun? We're up to 8.1.7.4 on Linux...