I replied to your email first thing this morning. For a quad of Zcon's on a pair of 5500's, to get the amplifiers to see a 1 ohm load, you are going to want to order dual 1 ohm voice coils. I suggest listening to what a few have said, at least in terms of space. Just because you had 4 L7's, that does not mean they had the proper air space. We have a few people with 5500's and 4 Zcon's, and they are all seasoned competitors with large battery banks, huge alternators (if not more then one), voltage regulators and are running walls for the Zcon's. There is no issue on ordering 4 Zcon 12D1's and a pair of Crescendo 5500's, that has some extremely high potential, BUT, if they are not given the proper air-space and supplied with sufficient current, it will be a waste of money. These are massive amplifiers that can easily put out ratted and then some, but they need huge amounts of current to do so. It would be like hiring Magnus VerMagnusson as your body guard, but only allowing him to eat two cups of rice a day and having one hand tied behind his back.