Glad to help. In case you have not seen it, there is a whole thread devoted to brakes on this Forum.
http://www.sr20-forum.com/information-library/30432-brake-thread.html
It has a section on brake upgrades in the third post that provides a link to a long thread on rear upgrades found here
Maxima Rear Brakes, Once and For All - SR20 Forum
I have upgraded the rears on one of my B13s. Before you do so, you really need to seriously ask yourself how you are going to use the car and think about why you may, or may not, want to upgrade the brakes. Honestly, street driving a non-turbo DE, the OEM system with good fluid, properly bled hydraulics, and a set of upgraded pads would give you more than adequate performance. That's my opinion, and not everyone feels the same way.
If you have a turbo, a VE, or plan to put the car on a road course, then a front upgrade is a good idea. The larger rotors and calipers give you a much bigger heat sink that will prevent fade in almost all circumstances. Since upgrading to the front NX system, I have had dead-reliable brake performance on road courses.
Getting into rear upgrades is the next step. I did this for my track car because I was getting some rapid deterioration of the stock Nissan pads that I was running. I probably could have done just as well by upgrading the rear pads. One issue that I ran into was trouble getting the E-brake cables to fit in the Maxima calipers. They go in there and they stay, but the retaining clips are not the right thickness so they fell out. That's not the way that I like to do things, but it is what it is.
From your name, I am assuming that you have a 1994 B13. I also assume that you know that your factory wheels will not fit over the NX2000 calipers with fresh pads. The wheels need to be swapped to aftermarket wheels or stock NX wheels. Otherwise, the calipers need to be ground down until the stock wheels will fit without rubbing. Just making sure that you are aware of this.
Also, if you order NX2000 calipers, make sure that they come with the mounting brackets. Most that are listed as "Loaded" will include the brackets, but it's nice to confirm with a picture or specification that includes the brackets.
Take a good look at the threads that I noted above and come back if you have specific questions.
Happy New Year.
Bill