Odd. There's nothing that Voladj does which should add distortion to tracks at low volume under those conditions.

Since you use the Kenwood to control the sound, does it also control the volume, too? In other words, do you leave the empeg at 0db and do all your volume changes from the Kenwood? If so, try setting the empeg to -10db or so, instead of 0db, and see if that fixes it.