[Pallando B.C]

The Istari were sent to Middle-earth to:

...contest the power of Sauron, and to unite all those who had the will to resist him.

and..

..were forbidden to reveal their true natures or to use their full strength in direct conflict with the Enemy

This means that the fires and voices you speak of were only 'minor' strengths of the Wizards. You could assume that since they were of Valinorean race, they had power, but did not use it whilst on Middle-earth.