There's 3 flavors to the MPC2000XL.
Base MPC2000XL
MPC2000XL Studio
MPC 2000XL Studio Plus
The base MPC2000XL differs from the MPC2000 in that it has WAV support and Time Stretching features.
The MPC 2000XL Studio contains the 8 out board (SMPTE/SPDIF reader/generator).
The MPC2000XL Studio Plus contains the 8 out board as well as the SampleVerb effects processor.
The good thing is that you can buy the base MPC2000XL and add the 8 out expander and the effects unit at a later time. The 8 outs will save you time (money) in the studio because you will be able to track out a beat in one or two passes using all of the available outputs. If you're at home and don't need to worry about being on the clock at a studio, you can do the same passes with the standard 2 out, but it will take a much longer time.
I have the Studio version and I have never worked with the effects board. I have never heard a good thing about it, so I never really looked into it.
I made sure that I bought the MPC2000XL Studio, because I have an 8-input soundcard card. When I track a beat, the 8 outs of the MPC go directly into the 8 ins of my soundcard. I can get my beat tracked into my sequencer in 1 or 2 passes (5-10 minutes). Tracking without the 8 out board would take me 20-30 minutes to get all the tracks seperated. If you're paying studio time by the hour, you can see where you can save money with this option.
If your soundcard only has 2 inputs, no need in getting the 8 outs board because you will still be stuck to tracking your beats 2 tracks at a time.
I've seen the 8 outs/SMPTE/SPDIF board for under $250. I have never priced the effects unit.
Here's some more info from AKAI's site
http://www.akaipro.com/consumersite/productpage2.asp?id=77§ion=options