OP.,,I looked at your system and you are using Accuphase A45 which is a 45w/ch Class A amplifier. In my experience, Class A amps sound their best at higher volume. They need to be pushed to open up. Soundstage width and depth usually corresponds with volume. At higher levels the stage will be larger, provided your room and components are up for it.
In my opinion you might want to consider the following:
High power Class AB amp (i.e. Gryphon, Pass, Simaudio Moon, Boulder, McIntosh)
More open and transparent sounding cables like the Nordost, Kimber KS, Transparent Audio, higher end Audience AU24sx or Front Row.
Purchasing higher sensitivity speakers may not accomplish the task here.
Also keep in mind the system that sounds great at lower volume may be too much of a good thing at higher levels. All depends on synergy
Just some food for thought.