the mm6 can only play one or two voices or two voices in keyboard split mode if you use the controls on the machine to select sounds.
however it is a 16part multitimbral soundmodule if it is controlled from your mpc or another sequencer - that means you can use 16 sounds at one time, each sound on its own midi channel.
to do this you have to switch drum to midi on the main page of the mpc, set the acording midi channel 1A, 2A, 3A and so on for each track. now comes the tricky part: to select different sounds on different tracks you have to use the no.1 field on the mpc. switch the number and you should get another sound. the problem here is that there are only 100 or 127 numbers but your mm6 has more sounds than that. so you hit the window key on the no.1 field and here you can set the msb and lsb numbers that are written in your mm6 manual for each of the voices.
i´m sure you have to fiddle a bit to get it going but this is the direction...
peace jo