I put an electrometer on the wire between the MV dynamo and the LV-MV step up transformer, and it reads 65 EU. So the dynamo makes 66 as I calculated, and 1 is lost in the wire so the transformer should see 65 in doInject() and go into overload, but for some reason it doesn't. I even tried eliminating the wire and just attaching the transformer directly to the dynamo and it still doesn't overload.
I think I found the error. It's in TileEntityBase11Bidirectional::readEnergyConverter():
tEnergyIN = new TE_Behavior_Energy_Stats(this, aNBT, mEnergyOUT.mType, mStorage, mEnergyOUT.mMin <= 8 ? 1 : mEnergyOUT.mMin, mEnergyIN.mRec, Math.max(mEnergyIN.mRec, mEnergyOUT.mMax*tMultiplier)),
tEnergyIN is supposed to be taken from the normal output values in reverse mode, and the minimum is, but the mRec is taken from the normal output voltage ( so 128 ), and the max is either the normal input mRec ( 128 ) or the normal output max ( 64 ), whichever is greater, so it ends up being 128. So an LV-MV step up transformer can actually accept 128 volt input packets. Which means you can actually hook it up to an MV battery box and it will give you that single amp 256 volt packet I was wanting before, and you don't even have to limit the input to 2 amps! Woot!
So basically going by the tool tips you should have to use an MV-HV transformer from a 2 amp limited MV battery box to get a single amp at 256 volts, but due to a pair of oddities in this TileEntityBase11Bidirectional::readEnergyConverter() function, you instead have to use an LV-MV transformer.