You can just connect over regular FTP and go to the appropriate directory. If you want to go direct to the addon with the new account, use the same server and port as your normal connection. You should only be changing the user. You don't need to set a root directory, and addon folders contain no public_html (they themselves are the web root for the addon), so leave that blank.
All I can suggest is going back to cPanel and checking the addon domain setting, perhaps deleting and resetting if necessary. Just to recap: New domain name: pixelrevolvere.com Username/dir/subdomain name: pixelrevolvere (although you can make this whatever you want) Password: (use your HU account password) Then login to your standard webspace via ftp, navigate to public_html/pixelrevolvere/ and upload your new site.
