...I guess you've tried Volume+ or one of the EQ apps at the Play Store?
Been known to help low volume issues. Jet Audio (and probably other music players) have built in eq's that can help tweak frequencies as well.
This here claims it will blow your speakers out ...so becareful if you have any pets lying around, speaker parts can injure and TFF cannot be held responsible for vet bills. Or grocery bills. Really any bills, now that I think about it.