umm, I may be wrong, but I think all you need to do is middle mouse [I work on a PC...] and drag from your first material onto the utility and choose plusMinusAverage1.input3D[0], then middlemouse drag from your second material onto the utility and simply choose whatever node is available next! This should be plusMinusAverage1.input3D[1].
I just tried it and it worked fine, let me know if this is what you are looking for?
I have never used maya3.0, but i am assuming it just didn't have a list of nodes to choose from? it just had "connect next available" and you'd click that and it would connect it to the input3D[1]....?