So far the most I've seen is my own, I couldn't find the forum that had similar. 11 for myself. though I know of only a way to get 15 lines of damage with a second ToD ring with Acid burst and the epic red dragon robes for the fire burst
From left to right on the longest line is Normal, sneak, icy burst shocking burst, holy burst, monk special attack, force damage ritual, frost, pure good, shock, and holy.
This was with using my +5 icy burst, shocking burst handwraps of pure good in conjuction with my new ToD ring with holy burst on it.