Accessing more multiple FTP servers through the same router

[nmargon]

I have successfully been using Core FTP Light to access our remote Buffalo LinkStation FTP file server behind a Netgear FVS318v3 router; we now had to install an additional Buffalo LinkStation Live FTP server, again behind the same router, both FTP servers listen on port 21.
My questions are:
1) In Core’s Site Manager, how to configure the 2 Sites so that I can selectively access either of the 2 FTP servers with internal IP 192.168.4.10 & 192.168.4.11.
2) How do I configure the Netgear router for Port Forwarding selectively to the 2 internal IP when both servers use the same FTP port 21.

Any suggestions and help will be most appreciated.

Nevio