In a couple of weeks I am going to buy these speakers from an eBay store. Does anyone own these or has owned them? How do they sound and what would be a good amp for these speakers? They have an RMS rating of 500w per channel @ 4ohms. I have read good reviews about these speakers but I am always skeptical when reading reviews from sites that actually sell the same product that is being reviewed or discussed. Also what is the difference between a speaker that has a rating of 500w @ 8ohms vs. 500w @4ohms? Which is better to use?