@richie: I guess its different cause AFAIK the MPC doesn't have a filter chip. The SP12 mod is probably directly connected to the filter chip of the SP. Since the SM2044 is a complete filter (adjustable filter with resonance) you "just" need to put a controller between the pins on that chip.
I guess the MPC mod is more like an extra filter (probably a SM2044 or the new one (released last year) that is put into one (or more) of the outputs. Therefore as you change the output of a pad you can choose if it runs though the one with the filter.