Do you have an MPC4000 yet?
Comparing the MPC2000XL Drum programs to the MPC4000 capabilities is complicated because the MPC4000 has much more power than the MPC2000XL. It works differently by using Multis, Parts, and Programs. There is a way to use more than one Multi in a song. To keep this explanation simple let's use a single Multi as an example.
A Multi contains Parts. AKAI recommends that each Multi should be created with 32 Parts or more. The maximum is 128 Parts per Multi. Programs get assigned to Parts. So there is a maximum of 128 Programs per Multi. The MPC4000 has 6 banks instead of 4 like on the MPC2000XL, which means you have a lot more sounds available to you.
Sequences contain MIDI data that is sent to either a MIDI out or the Sampler. The output is specified in the Main window. Send the data to a MIDI output when using an external device such as a synth. Send the data to the Sampler (by specifying a Part) when using samples. A pad hit is just another MIDI event that triggers either the sampler or an external module.
To view the sequencer assignments of the MIDI out and the Sampler access the MIDI mode. Change the routing while viewing this screen. You will see a routing line change position as you change the assignment.