Hi Daniel
The P2055 printer is not able to receive a file by the FTP method so spooling an rfu file will not work. The bin file you mentioned is such a file but it cant be sent down like an executable file. It needs to be sent by the utility program on a Windows or Mac device.
To get the firmware updated, add a Windows or Mac PC to the network. Setup the user with Full Admin rights so the user can see all the printers on the network.
Install and run the utility and it will list all the printers available, choose the printer to be updated and it will apply the firmware.
Its a longer method and needs to be done one at a time. Try this on one or two printers first and let us know how you went.
Steve Hewitt
HP Australia