When I bought my Z3 last December, the subwoofer speaker was not there...but there are 2 pairs of wires entering the box where it should be. I connected a speaker to each pair separately as a test, and both pairs operated the speaker quite nicely to my surprise, so it appears that the amp is functioning okay. I am going to buy a speaker to fill the hole and my question is...what speaker has 2 sets of connections for the 2 wire pairs? Also, am I looking for a 2 or 4 ohm speaker? Appreciate any insight!! Thanks! Kevin