Just a quick tip, I just discovered this and I thought it might help some of you.

I had a melody with notes from D5 to C7. And my lead was made of 2 layers, where one of them was lower.

Now in the middle of the melody I had the volumes right and it was a very nice fat lead. But when the melody was in the lower notes the lead had too much lows and in the higher notes the lead was very thin and bass lacking. So I just volume automated the lower layer with the notes.

I was using studio headphones and I am not talking about a bass, its just a a lower octave supersaw.