I really don't know what your budget is.
Well if you got the mpc 4000; then you should hook it up to decent equipment.
A very basic inexpensive mixer is the mackie 1604.
www.mackie.com; www.musiciansfriend.com; www.samash.com (compare prices)
If you want to go digital there are a dozen options. I love Yamaha mixers; in particular the 01v.
The main outs of your mpc should be plugged into available channels on your mixing boards via 1/4 inch ex: channel 1 and 2. if you have the 8 output expander continue channels 3 - 8. Your sound module should have stereo main outs and 4 more outputs. Plug those outputs to available channels on the mixing board.
If you are desperate and have a dj mixer; get 1/4 inch to rca connectors and plug them to the inputs on your dj mixer. This really doesn't do your equipment justice but good for you to practice till you have the dough for the gear u need.
Peace