Your problem is not VOLUME. Its Percieved volume. Because there is no low end to carry the mix it sounds Low in volume. It almost sounds as if everything in the mix is high passed at 100hz or so. You have NO subs going on.
Fix your EQ settings and you will notice a BIG difference.
There is a HUGE difference between actual and perceived volume. Dont use your meters at a reference, use your ears! You can have 1 mix that is at -6 RMS and another that is at -10 RMS and the one at -10 can seem vastly LOUDER then the one at -6 if the low end is bigger.
Audio production is all about using YOUR EAR and not presets and OMG THIS MIX HAS TO SIT THIS LOUD IN ORDER TO BE GOOD ... Fuck all that jazz. Do what sounds good to YOU and go with it. Thats how you develop your own sound and style.