I've got to sideline on the volume part... There's a reason why so many mix ~85dBSPL (the point where human hearing is most 'flat'ish). I'm not saying to mix there and stay there -- But if you're mixing at ~70dBSPL, there are things you just aren't hearing -- And I'm not referring to the spectral imbalance.
It's not rare at all for me to get projects in that are absolutely riddled with clocking errors (etc.) that are obvious to the ear around 85dBSPL -- and at much lower levels once they go through the garden here -- that are essentially inaudible at lower levels. Ornamental percussives that might sound perfectly fine as far (as volume balance is concerned) at low SPL might be screaming hot at higher levels -- And once balanced at higher levels still sound fine at lower levels.
If it sounds good at 70dBSPL *and* it sounds good at 95dBSPL, it'll probably sound fine at any volume. But if it sounds good at either of those extremes, it might sound terrible at the other.