Splitting cables is meant to split energy into two halves, which is great, but it loses energy if the input is an odd number. For instance, if burning coal in a generator and splitting the output to two MFE's, the total energy burned is 4000, but the total energy gained is 3200. This is because the generator outputs at 5 EU/s, and each 5 EU "packet" of energy is immediately split into two 2 EU outputs (since EU's need to be measured in integers), losing 20% of the energy!
Rather than giving each output half the energy of the input, one output should be given half the energy, and the other output should be given the rest. In this case, one output would receive 2 EU, and the other would receive 3 EU. Ideally, it would alternate, to keep things even on average.