In your sound settings, there is a "master" sound -- the System Setting -- that all the others work off as percentages of this setting. Make sure this setting is at the max and then adjust all the others accordingly.
I haven't been able to find this setting in the X's native settings (Settings > Sound > Volume), but I downloaded the app Audio Manager Pro (99 cents)from the Market and you can access the System Sound settings from it's excellent and colorful widgets. Worth the bucks.
ALSO, check in Settings > Sound > Media Audio Evvects > wired stereo devices &/OR Phone Speaker. In Phone Speaker, you can enable audio effects and set the equalizer for vocalizer. Both these will help out enormously.