I have used Niles in many instances. I do not have loads of experience with the rock speakers though. They normally have an outstanding product. I would contact Niles' technical support to see if there have been any other issues with them, as well as work with your local dealer to see if your's is an isolated scenario.
When you returned the first pair, did they tell you what the problem was? I always let my customers know what the problem was with any product. If it is a manufacturing defect, you should know about it. If it was the customer's fault, they should know about it.