I've searched for "dalaran brilliance" but haven't found anything, so I guess that wasn't posted here (correct me if I'm wrong)
As you probably know, there are 2 different versions of the +x% Spellpower Buff. Those that give +10% like the one an ele shaman and demo locks bring, and a 6% version from mage's arcance brilliance and flametongue totem.
Both usually don't stack, so if you have a ele shaman and a mage, you only get the 10% buff.
But if you let your mage cast Dalaran Brilliance instead of Arcane Brilliance, those two buffs do indeed stack.
As far as I know that works for any +% SP Buff coupled with Dalaran Brilliance, so enjoy your free 6% as long as it doesn't get fixed.