You can enable and disable your spam box from the same page as SpamAssassin. It's just that easy!
With the recent upgrades to cPanel, the team has been paying more attention to the users of SpamAssassin.
In the previous build, you would need to use an IMAP client to get to your spam box. Well not anymore. You can create a "new" e-mail account that has precisely the same settings as your e-mail account, but add: "spam" to the end of the e-mail account user name. This will retrieve only your Spam Box mail.
You will want to set up your e-mail client to deliver this Spam Box mail to a special folder (perhaps called spam) automatically.