The MPC 2000XL is much more a sequencer and sampler than just a groovebox.
The SP808ex is a groovebox, sampler and 4 track recorder. The SP808ex is very much a remixing tool, both live (16 pads I believe) and an actual remixing tool.
You have 250 mb of disc space to place a track on and the SP808ex can recognize the bpm and make you other samples fit the same tempo.
The MPC 2000XL is more of a studio tool. It's supposed to be the main base of your studio, controlling the other devices via MIDI.
HI, mpc 2000 xl is good for Rythem tiggering, the 16 pads onboard are used to tigger, and the sp808, is a 8 cahannel mutltirack harddisk recorder, and has 16 pads to mix and sync rythem, u can import any rythem from u're computers to the sp 808 with the given onboard zip drive. if u're do live then go for sp 808 otherwise go for the mpc 2000xl bothe are good ***.