Lance, another welcome to Axiom. You've already gotten some good suggestions here, but depending on the extent of your hearing damage, none of the adjustments that we suggest may be enough. I'm certainly not an expert in this area, but I've done quite a bit of reading on hearing damage from high sound levels and have noted with dismay some comments on various audio forums about "liking it loud" and referring rather casually to extensive listening at levels in the 100dB area, which is well into the danger zone.
Many center channels in movies are mixed at a low level with respect to the other content, and making a 3-4dB boost in the center from the balanced level set with test tones can help with this part of the problem. Your situation however compounds the difficulty by apparently adding losses in the upper mid/lower treble frequencies(about 2-6KHz, see
this brief discussion ) which affect the consonants most strongly and can make speech intelligibility poor even at loud levels.
It's highly unlikely that a speaker with a "colored" mid/high frequency response could be more than at best a hit-or-miss proposition with its uneven or distorted response "correcting" the problem in differentiating the consonants. The Yamaha that you're getting may be more helpful in that it has, as do most receivers with equalizing circuitry, a manual Parametric equalizer option which can be set to affect a few specific frequency bands. Try setting the center channel band or bands in the 2-6KHz consonant area up maybe 5-6dB.
