I wouldn't even try eBay. You could try selling them in bulk on craigslist if you have A LOT. You're not going to be making the $80-$100 like you would on eBay but, it's better than having to worry about all the legal issues. Depending on where you are craigslist is a very good way to get rid of inventory fast.
If you must sell on eBay you could hide the listing from P90X themselves by listing the item in different ways and avoiding them sending letters at all. Maybe something like "Extreme Home Fitness P 90 X" or use the P90X as ²P²90²X². This isn't guaranteed to work, but it's better than nothing. You also gotta realize that you run the chance of getting you're account suspended.
As for the address, unless someone has been in your exact situation there is no way of knowing. Your best bet is to call up eBay and ask them yourself. Not about the P90X or whatever just ask what address do they give out for legal matters.
__________________ “You have to learn the rules of the game. And then you have to play better than anyone else.”
-Albert Einstein |