As an addition to my last post the associated amplifier being used to drive the Overkill loudspeakers was also by Overkill.
Reading through a few posts on this thread I noticed very few respondents mention the associated amplifier being used to drive the speakers that left such an impression. Perhaps, to the best of their recollection, past and subsequent posters can include this very valuable association to the experience. The reason being several of the loudspeakers mentioned I have also heard and, at the time sounded not so special. I heard the Focal Grand Utopia's powered with class A rated Spectral mono's at a dealership in Santa Barbara that sounded (for me) awful; shrill and painful. Yet with the right amp and associated gear the FGU's can sound exceptional. Electrical synergy that translates to emotional and component harmony is key. As we all know a speaker is only as good as what the amplifier is doing for it primarily and what the room is doing additionally.