Technically not, each kit will have perfectly matched memory to be used in a single system for optimal performance. It is possible to have two kits that do not work well together, so keep this in mind. But since you already have a kit, go ahead and get another one to add and take that risk. If there is any problem, contact us directly, we can troubleshoot and provide a solution. We will make sure 16GB is working flawlessly in your computer.
Two identical dual channel kits is the same as a quad channel kit.