I have tried installing on three different machines, using each of the different installation methods you describe. No success at all. My system complies with or exceeds your requirements.
Debian Wheezy - once on a local dedicated server, and once on a VPS. Both times this same error of "Unable to locate package sourcefabric-keyring". I even tried installing it on a Windows Apache server and got the same error (as well as few others).
Where is the package sourcefabric-keyring? It does not appear to exist or else is not in an accessible location,