After installing Rear Maxima brakes (semi-metallic generic pad) on my NX with AD22's up front (Axis Ultimate pads with 80% left) I also installed Altima brake master cylinder and noticed the following:

- the brakes do not bite as hard as before (I bled the brakes with fresh Motul 600 fluid)
- During braking on track (small tight track) it seems like there is too much pressure going to the rear instead of front brakes- I almost rammed a car from behind several times as the brakes did not have a good bite (last year same track I was able to brake harder with rear NX brakes and stock master cyl - same front pads)

The Question:

Should I change the master brake cylinder to the stock NX one for better front bite and better brake balance? Thanks.

If you're using the Altima proportioning valves you are now at 853 psi front and 483/540 psi rear. The NX was at 995 psi front, 569/626 rear.
You could try switching proportioning valves as long as the master cylinder is the same brand. On the Maxima rear brake upgrade thread it said the " propotioning valves are dual proportioning, so it controls front and rear, even thought it's threaded into the rear output bosses on the m/c."
You may want to start with the NX front valve first and go from there