Most “disappeared” speakers.

Agreed that almost any, or most decently designed speakers can "disappear."  Though some do it much more readily and successfully than others.

A good bet is for the speaker to be time aligned and put in the room so as not to screw up the phasing.

I second georgehifi’s comments on Audio Physics and ESL’s.   I own ESL (X-Static) and the only other speaker I’ve heard that comes close and is musical is the Audio Physic Tempo Plus.

Also, agree that the room, placement, equipment, cabling, source all matter as you are listening to a “system” not any one Componenet.

I am chuffed to bits with mine an ex dem pair of Piega Classic 40.2. Superb ribbon tweeter which just gets the music right. I use these with valve amplifiers which really assist with the staging. Prior to these I found Living Voice did a reasonable job. However the Piega also pass the wife test which is important. 

Boenicke W5 can do this well. Also have impressive bass för being so small. 

I agree that Audio-Physics are also good at this.