You could if you configured both Filezilla servers to allow FXP, use a PC to control the transfer between the two.
Alternatively, Avalaunch Dashboard will quickly set up the Xbox's for you so you can connect them together and then FTP from one to another - it has an FTP client aswell as an FTP server.
XBMC as far as I am aware only has an FTP server not a client so couldn't be used this way - neither does it have an SMB server - it has an SMB client only.
I think your best bet is to use the Avalaunch dash.
HTH
Nick