Individual album discs -- or tapes -- are now represented in a new media table. This means every piece of media now gets their own catalog number, and you can specify a mix of media formats (such as CD + DVD) for a single album entry. The change is mostly internal at the moment, but eventually media catalog numbers and titles will make their way to album/tracklist displays and search functions. Media entries are also automatically synchronized with the total number of tracks and total playing length in associated tracklists, which will be required for an upcoming top-secret feature =)
Album submission is still largely unchanged. You specify a format and the number of discs, which automatically creates the media entries. If you specify a catalog number range like CPCA-10128~34, the system will automatically split it up for you. Afterwards you can modify existing media and add new entries through the album edit page (note that you must click on the submit button for the changes to take effect). The latest media submissions can be viewed from Recent Updates.
Click here for a screenshot of the interface.