AC Generator for maximum load
Don't do it! As commented already, the current can be too non-uniformly distributed due different resistances. In addition:


Have you already checked that the outputs really come from the same winding (=in parallel connected windings) in the single voltage mode? The actual generator in the machine must be extremely precisely made if there's parallel windings.
If yes, then how you can be sure that all output connectors to your single load stay connected and none is ever reversed? 
Have you checked what happens if the machine is in 2 voltage mode and the outputs still are in parallel?


If one or two pops out or get damaged, something can get overheated without warning. Reversing = Short circuit. 

The manufacturer would never allow your planned connection because they should pay your burned house if they allowed the connection and you left 2 outputs disconnected. 

User Transistor had added something essential: Unplugged parallel connector has full voltage. => If the manufacturer allowed your connection, they should also prepare to pay the possible funerals.