crikey, a fair echo in this thread. at least everyone agrees that tires are important. if you are going to stick with N2 tires, i am afraid that you are always going to struggle for grip - and that in itself will be realistic.
On the LSD, you will have to work out where you are having trouble. if you are loosing traction on power, fiddle with your accel number (up or down as necessary), if it is during breaking fiddle with your decel, and on coasting - fiddle with your initial. General rule i use, is that if you are understeering in any of these states lower the number. if you are oversteering in the state raise the number. Eg if you are oversteering on corner exit, INCREASE your accel figure.