Unfortunately, the core five channel amps are not assignable. Using an external amp for the fronts would mean leaving the Front speaker channel terminals on the Denon unconnected and those two amps would go unused. You would still need another external amp for the second pair of Height speakers. I don't believe the X4100W allows for a 7.1.2 configuration for atmos. I think the choices are 5.1.2 using only the internal amps or 5.1.4 with an additional amp.
