You are not able to add the power of both channels together to achieve 400 watts, you are simply driving each section of the speaker with 200watts, this makes it better for the low frequncies, as you have a full 200W available to the woofers instead of a portion of the 200Watts when single amped, other than that there is no advantage.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70