the FAQ states the following
special abilities that require you to spend surges are designed to stack. so if you have an ability such as "surge: +1 damage and pierce 1 and you pay 3 surges, you gain +3 damage and pierce 3.
cone of fire has the following abilities
breath
surge: +1 damage
surge surge: burn
can four surges be spent to add 2 burn tokens to a single attack?
our group was under the impression that this could not be done as burn is not a ranked ability like pierce, aura, etc ... and that for that reason it does not stack.