Playing the Roland Jv-90 with the Mpc...PLEASE HELP!!

Ok I figured how to hook everything up by myself, I learned how to make a drum pattern, loop and hooked up the keyboard and made it the slave. I figured all of this out but now i am really stuck. My set up is extremely simple. I have a mackie mixer hooked up to the mpc 2000 which is hooked up to a roland JV-90 keyboard. Whenever I make a drum pattern and then want to add the sounds from the piano, the mpc loops it. Here is where I get stuck. I loop a sound and then I go to a different track to add a new sound and overdub. When I change the sound on my keyboard the mpc loops the new sound to the same pattern of the last sound I played. It seems like I can't add a new sound to the loop if I change to another sound on my piano. I don't have this set up to a computer or any type of input to record the last sound I played...is that it? Do I need a program on a pc to record everything i play so I can add on to it or does the Mpc allow me to play one sound from the keyboard, loop it, record it, play it back while I add another one...and so on and so. I thought this was called multi tracking but I can't figure it out. Any help would be greatly appreciated.