It is possible to migrate to the next higher hardware model, but in your case the supported destination model is the F400. If you are using a Control Center you could migrate to a F400 and then from the F400 to the F600 in a two step process.
For a standalone firewall you can still import the PAR file, but you will have to configure the required changes manually. Depending on your firewall configuration it may be faster to reconfigure the F600 from scratch. You can also get in touch with our technical support to help you with the migration.
Edit: You must migrate the PAR file before just including it on an USB recovery stick.