Though I have no experience with EU in 1.5.2, adding the transformer shouldn't make a difference.
The electrical engine can accept all voltages of energy, aside from ultra-high and will produce the same amount of power, regardless. The only problem I can see from this situation is that you don't have enough energy going into your MFE. How you've set up the MFE -> Engine part should be correct, which leaves the EU -> MFE connection. How are you generating this EU?
I don't think you are required to generate 256 EU/t, rather you need at least 256 EU in your MFE every time the engines request energy from the MFE, since the engines will be requesting 128 EU packets from the MFE. To my understanding, if you look at the pulsing bar inside of the ee's interface, you will see that it'll pulse more slowly as your EU packets get larger. This is where I have come up with this conclusion.