perhaps I'm off here, but I believe 'stacking' is what many headphone amp designers use to to achieve higher current output than available from a single chip alone. Literally stacking DIP chips on top of eachother. Not many MOSFET drivers are available in DIP's anymore though.
Just googled your part numberse, they're relatively slow switching bipolar transistors. I imagine they are configured in a 'totem pole' a classic way to drive MOSFETS. Bipolar transistors can be paralleled for this (I think) but as they are essentially current amplifiers, you would need to drive these with more current...which may require yet another stage to give each transistor a high gain.
As crutschow pointed out, driving a MOSFET is all about the gate capacitance so you need to know what these big MOSFETS are.