Never used an isolation box...but doesn't such a system, by design, pretty much eliminate the unique reverberation and complex reflections of a particular "room". I mean, isn't an iso box basically a miniature anechoic chamber?
it removes the room reflections but not the "air movement" between mike and speaker.
in fact its a "little room".
its not perfect , but its a lot better than an emulator , IR´s etc.
ive build an cheap iso-box but only to remove the room ambience from the mikes , and it sounded really good, but off course
didnt resolve the volume issue.