not sure how old this post is I was just browsing the forum....
The easiest way to create a multisample pack from an external MIDI instrument is to automate the process.
Use a program like
http://www.samplerobot.com/ which will automatically trigger and sample the output of any MIDI synth and save all the samples into a folder on your computer. All you do is set the range of keys you want to sample, the number of notes per octave, and the number of velocities per note and press go. It automatically takes care of the rest saving all the files with useful names in a folder on your computer.
Then I'd use a program like
Bluebox to automatically create programs for the MPC500 from the samples in your folder. You can bulk load all the samples you created into Bluebox at once. Press a button to make the pads chromatic and then save your patch into the same folder as the samples.
Connect the MPC to PC with USB and drag the folder over. The whole thing is done without having to manually record, edit or keymap any samples. By doing it this way you would get 10/15 new programs from your Fantom in the same time as it would take to get 1 by manually sampling, edting, mapping. Also you do not have to squint at tiny screens for hours laboriously sampling in one sample for every pad.
cheers
Grizzle