I dont think youd wanna go trade all that in after you just bought it. Your decision though.
I'd say get a sound module. An E-MU sound module. If you didn't know it, getting the sound module keeps you from paying extra money on features like a sequencer and other stuff. You dont need another sequencer, because you already got the MPC.
E-MU:
"E-MU's 30th Anniversary Proteus® 1000 is a powerful 64 Voice Expandable Sound Module that celebrates the legendary sound quality and cutting-edge synthesis features of the Proteus 2000 in an affordable package. Proteus 1000 offers you the same 32 MB Composer soundset and lightning-fast processor as the Proteus 2000, delivering dead-on MIDI timing for your most complex sequences. Proteus 1000 also provides you with an additional 32 MB ROM slot, so you can expand your sounds using any of the available Proteus ROMs ... you can even author your own custom sound ROMs using E-MU's E4 Ultra samplers! The 12 programmable front panel controllers allow you to perform and record a host of parameter changes in real-time, giving you total control of your sounds. Proteus 1000 gives you all the power and flexibility of a legend at an unbelievable price.
64-voice polyphony
1536 presets (1024 ROM, 512 user)
4 layers per preset
32 MB internal sound ROM
One 32 MB expansion slot (up to 64 MB total)
16 MIDI channels
24-bit dual stereo-effects processor
4 real-time control knobs (12 parameters)
2 analog outputs
16 part multi-timbral
SoundNavigator
Super tight MIDI response"
http://www.musiciansfriend.com/srs7.../g=rec/s=computer/search/detail/base_id/59703
check that one out.