My low beams turn off also when my highs come on.
When my fogs are on and i switch to the high beam the fogs and low beams turn off
Here is why:
If you look into your main headlight you only have one bulb. There are two fillaments in that bulb, one for the lows and another for the highs. If you were to wire it so they both stayed on at the same time (i think this is actually impossible correct me if i a wrong) your bubls will die and you be singing a song like this
I am not sure if ghoster understands your question or if he made some kind of mod to let them come on at the same time.
If you just want more light add some 55w driving lights