The symptoms point to an environment problem. But, as the store offered to bring you a receiver from another, then give that a try.
Room correction can be a helpful tool. Most of us have listening areas that interfere with the optimal presentation of sound. Room correction makes adjustments based on the specific issues in the space, improving the sound for movies, music, TV, games, and whatever else you are listening to. YPAO is the Yamaha room correction product. Audyssey is the one that Denon and Onkyo use. The fact that the Yamaha has YPAO and the others don't have any room correction software is a selling point in favor of the Yamaha.