Speakers that disappear

Same theme in the responses here, Room treatments, Set-up, and Synergy. 

Not sure of your budget but another idea would be the MBL 126 I have not heard it but it does get incredible reviews and seems to have the traits you are looking for. 

+1000 to everyone who mentioned synergy. I have a story for you from last week.

A friend owns a number of speakers. Focal Utopia Scala Evo, Dynaudio Confidence 60 and Dali Epicon 8. This story is about the Dali.

He is fortunate to have access to numerous components from many different manufactures. Every time a new piece arrives we have a listening session where we try all three speakers and compare against his reference. 

In every case, the Dali was forward and the speakers never disappeared, regardless of placement. This changed last week when his new reference amp and preamp arrived. 

Not only do the Dali disappear, but we preferred the result of this combination over the other speakers. They went from being my least favorite to us thinking the new Epikore 11 could be his new end game with this combo.

Synergy is everything. We have had many huge lessons at his place with the ability to have so much gear come and go, but this ranks possibly at the top in terms of a 180 from a single component change. I say single because it was the amp, his older preamp resulted in the same disappearing act. 

@willy-t wrote, "pick music that doesn't have widely panned instruments and or vocals"  Oh man you hit a nerve there for me!  This is one of my biggest peeves.  Sound engineers often try and do too much and overwide panning has ruined too many songs that we all love.  I find that when engineers try and spread the mix as wide as possible the sound gets trapped and never releases from the speakers and just makes mud.  

For the OP to realize his goal when auditioning new speakers I would recommend that he hand picks some tracks that are very well recorded and that are known to produce a good sound stage.  I would look for music recorded by Alan Parsons and Ken Caillat, they are two of the very best at getting good sound that allows the speakers to disappear.

One other thing to keep in mind when auditioning is that more complicated music with more band pieces is harder for the speakers to render.  Simple acoustic or small ensembles can be successfully reproduced by any entry level Best Buy speakers but the bigger more complicated stuff will separate the wheat from the chaff during your demos.  Good luck and cheers.

check out the monitor audio platinum 100s if it's in your budget or the gold 100s.