aye, with an item that size its not expected that you will keep the box, so if its faulty they have to take it back regardless of packaging....
if its not faulty, well, if you had the box they prehapsibly might take it back, but without the box i'd be surprised if they did......a more specialist hifi shop more than likely would take it back...but a big chain retailer doesnt have too, a purchase like that should never be made without a serious think....