Many thanks to all those who have provided some excellent insight. I just thought I would provide a update and address one of the interesting points which a few of you raised.
For clarity, I thought a bit more context might be useful. So basically, I love the sound of the MM style bridge pickup (both in dual and single coil arrangement) - it is everything I would ask for for a pickup in that position. What I have come to realise is that I am mostly disappointing with the J style neck pickup. As the blend knob is turned towards the neck pickup all the gutsy, potent aggressive sound of the MM pickup is lost and replaced by a less defined, almost flabby and less precise tone - this is the sound that I am currently unhappy with and wish to have amended.
A few of you mentioned about replacing the pickups and I am beginning to suspect that this might be a more suitable approach. In light of that, does anyone have any recommendations on suitable J style pickups that might provide more of that aggressive and grunty sound (must be available in 5 string).