Are there speakers that disappear regardless of the recording?

I would think a lot of this depends upon how things are set up and what is in the room.  Actually, there is a dealer here who specializes in Master Set.  They demonstrated this in their showroom.  You couldn't detect either left or right speaker.  

Count yourself lucky.  You must have a nice sounding system.  You might consider adding a pair of REL SHO subwoofers.  Their high-level connection allows them to play like woofers.  The trick is to dial them in until you cannot detect them.  I have a source where you can buy them brand new for about half the price.  If interested, I could let you know my source only if you do not divulge the source. 

I have noticed some recordings produce more db at the same volume settings.  I am not sure why.  I often have to adjust the volume on my amplifier downward.  Perhaps this also reduces distortion?  Certain recordings just sound better.  I have a number of recordings I play to show off my sound system.