can you staple 5/16" engineered hardwood over 1/4" lauan thats covering partical board. or should i cover the lauan with more plywood.

I think the question is should you staple to luan that is over p. board. Most manufacturers and both the NWFA and NOFMA say no. However, if the luan underlayment is well attached to the p. board, it may work out ok. I generally do not recommend stapling/nailing into or through p. board. The best thing to do would be to remove the particle board before installing a hardwood floor to it. Not the easiest, I understand.