Can't speak to this particular fermenter but counter pressure is the way to go for sure.
Make sure the kegs are clean then completely
fill with no rinse sanitizer or treat with sanitizer and then fill completely
with boiled water. Complete filling is done to be sure that all air is displaced from the kegs. Then blow out the liquid with CO2 and pressurize the keg to 10 psi or so above the pressure in the conical.
Depending on the configuration of the conical you will have pressurized it through a carbonation stone or the CO2 bleed port and will be drawing the beer from a racking arm or standpipe or even from the bottom in which case you would have blown down settled yeast a couple of times.
Connect the beer out port on the fermenter to the liquid port on the keg but don't open the beer valve yet. Connect a keg filling device (http://www.pbase.com/agamid/image/122950815
) to the gas port. Open the needle valve on the keg filling device and allow CO2 to escape until the pressure on the gauge reads a couple psi below the pressure in the fermentor. Now open the beer valve and close off the filling device needle valve. The filling device gauge will gradually rise and then stop. Open the needle valve again. CO2 is being pushed out as the beer is flowing in. Monitor the filling device pressure and adjust the valve so the pressure does not drop more than a couple of pounds below its peak reading. This is to minimize foaming in the beer.
The receiving keg should be placed on a tared scale before admitting beer. Use the scale reading to determine when the keg is full. A liter of beer weighs SG kg where SG is the specific gravity of the beer.
If you don't have a scale then judge fullness by placing your hand on the side or top of the keg. You will be able to feel the beer level through the thin metal. The colder the beer the easier this is to do. If the beer is cold enough you may see condensation on the outside of the keg and that makes the filling level pretty obvious (works best on kegs that are not too badly bunged up).