On the contrary, you sounded really both kind and professional explaining your impressions and critics!
Anyways, the problem with vocals is mainly depending from the quality of the fourth song and I couldn’t fix it really well, even using gain and mid knobs!
By the way, I’m using 2 decks at the moment, since I own a Traktor Kontrol S2 (I told it just because you were talking about a 4 decks live 🙂 )
Thank you for your opinion bro!