@Motor city madman I bet you had the loudness button depressed.
Just kidding! Ah, lovinthehd beat me to it.
One thing that might help is to listen to only the Sansui for a while. When switching back and forth it's easy to have perceived bias. You can help reduce perceived bias by getting used to the receiver for a while, like over a weekend, playing a variety of material. When the euphoria of having nice vintage gear wears off, switch back to the Yamaha in pure/direct mode again.
There can be issues with simple listening tests though. Please allow me to elaborate. I would assume that the Yamaha and Emotiva have relatively flat frequency responses, given that they are modern amps. What if the Sansui has a bump in the lower frequencies? That receiver is going to sound like it has better bass output, when strictly speaking it is not really better because it is not as flat (and most audiophiles seek that truly flat response). What you could be hearing is colouration in lower frequencies that gives the impression of having more depth and punch. So it's not a matter of one being better than the other, but one having a frequency response that happens to be more to your liking. If the Emotiva has 200W/ch I doubt that it would be lacking dynamic range as the Sansui only has 125W/ch by comparison.