how are we supposed to know if you changed the voice coils or not?
we really have absolutely no idea what those speakers are anymore.
maybe somebody here has heard them when they were 3-4 years old.
now they are 10 years old no?
if you used them a lot ... or if time has let them age ... maybe they sound different.
timbre problems can be blended to create one new timbre if the phase and/or excursion allows it.
you could say one speaker is beautiful and the other is medium, and blend them together to create one big monster.
not going to happen without some reverb, and maybe you need some chorus too.
time alignment could always help.
if your room is big enough.. you could fill up one area with something much more cleaner than the muddy sound that gets trapped in the corners?