Sorry, I didn't define my term I guess... A secondary depth cue is one that is recorded into a song... reverb, room reflections in the recording venue, etc. Primary depth cues are ones that you hear directly in real life... location of the speakers, distance from the music being affected by the room acoustics of your listening room, perceiving location through moving your head, etc. A voice spans multiple octaves and consonant sounds can go even higher. An imbalance that made a vocal sound quieter and more distant would be so big, the drums wouldn't sound right, the guitar wouldn't sound right, nothing in the range of frequencies spanning the human voice would sound right. If it was just a part of the range that was affected, it would sound like the singer wasn't pronouncing consonants or the voice would sound thin or sound thick and muddy. When I turn the volume down on my stereo, it doesn't sound further away. It just sounds quieter. In order to sound distant it would need either secondary depth cues or actual physical primary ones. A balanced frequency response is a great thing. It makes the sound full and strong and sparkling all at the same time. It eliminates masking of frequencies and can reveal detail, but I really don't see how it affects soundstage, especially in headphones that really don't have any soundstage to speak of.