which powerconnect do multiple monitor (sniffer) ports?

I need to be able to do multiple monitor ports on a switch (e.g. port 1 sniffs port 2, port 3 sniffs port 4, etc..  The 5324, 5424 and 6224 I have now all seem to be limited to a single monitor port.  The 6224 software calls it a numbered "monitor session", but only lets me configure one session.  Is there an OS upgrade to get more?  or which PowerConnects can do more than one?