You have to think in waves of energy, and flow in cfm. The way I see it, you at worst have two converging flows without the butterflies. Each of these will be at a lower velocity than the originals, but total volume may actually go up. You could also get some extra turbulence from the converging flows.

Now look at the helmholtz waves. The runners are different lengths to tune the helmholtz effect at two different rpm ranges. Long runners for low rpms, short ones for high rpms. The reason for this is that the helmholtz waves propogate thru the air in the runners at a constant speed. In the intake, when the valve opens, it creates a region of negative relative pressure that propogates thru the air medium at the speed of sound. When the vac wave hits the end of the runner tube(s), it reflects back down the tube, but as a pressure wave instead of a vac wave. If the runner length is tuned so that the returning pressure wave hits when the valve is still open, it shoves some more air into the cylinder than just the runner flow would allow. This pressure can approach 10psi. Now you have two sets of waves. One set hits at the right time. The other set hits wrong, at least at that rpm. The waves may also be slightly weaker from being split into two runners. Dunno.

All that said, I don't think that any power loss is worth even hacking a $40 JY manifold to try to get it back.

Just turbo the damn thing and quit having to worry about Helmholtz effects to fill the cylinders...