Well the best way to power any added lights is by using a relay.
Power for the new lights can then come directly from the battery for maximum voltage.
The question than becomes what to trigger the relay with. The trigger could be any existing switch that provides 12 volts. If you want to run them with the headlights than use the headlamp power wire for a trigger. If you want to run the new lights without the headlamps than use a 12 volt switch that can be used independantly of the headlights..Perhaps the parking lights. Another option is a new switch powered from an accessory wire.