MYD and MYI files are raw MySQL table files. On their own, you can’t do much with them. phpMyAdmin definitely can’t do anything with them. As part of the entire MySQL data directory, you can restore an entire server. But no hosting provider, or any other provider that manages the MySQL server for you, will let you touch the MySQL data directory.
Also, 6 GB is a pretty big database. We don’t have a hard cap on the size of a database here, but I think you’ll run into trouble with a database that big.