The Yamaha rxv663 is a 7.1 AV reciever.
Sounds like a setup issue with the 663 to me. You may have a surround scheme selected and your vocals are being sent to a center channel speaker.
I have my cornwalls in a 11x14 room with them on the long wall, in the corners, toed in, pointing exactly at the listening position ( around 30 degrees)
Sound fantasctic.