the XL is basically a 2000 ... but with better features.
some of those features:
-the xl has time stretching, though it is slow and not very good compared to computers
-the 2000xl can read folders on cards etc... this is very important and one of the biggest additions to the mpc line that was not previously available... especially when:
-the 2000xl has an IDE/ATAPI port which makes it cheap and easy to install a CF reader, instead of having to try and find a 100+ dollar scsi cf adapter
-the 2000xl has dedicated buttons for changing pad banks.. now you no longer need to push the one button four times to get to bank D..
-the 2000xl has a track mute and solo screen which allows for easier and better performing track mutes and solos for live use... it is also visually easier to see what is muted and what isn't all one one screen
-the 2000xl has a cool jog wheel feature that accelerates the longer you spin it, so when you are trimming samples, it's like it has an automatic transmission that changes to a higher gear if that makes sense... the 2000classic does have the better jog wheel and you use the outside part of it to switch digits for going faster.
-the 2000xl has a feature in trim mode where you hold shift and slide the NV fader/slider to move the cursor quickly to a general area of the waveform and you can use the jog wheel to do all the fine tuning.
-the 2000xl is easier to get into the machine to do addons and maintenance because you only need to take off the bottom plate instead of removing the top casing and dismantling the pad assembly.
-tilt screen makes for better viewing angles and apparently the screens last longer because it is easier for heat to escape... I dont know how true that is though.
-the 2000xl doesn't need a boot disk, the 2000 classic does... not a big deal though
-the xl came out in like 2000 or 2001 or something like that... the 2000classic came out in 97..
-the 2000xl has resampling, but not the kind you have in other machines.. in the xl it allows you to change the sample to a different bitrate. this is as slow as the time stretch (you click "do it" before work, and it might be done when you get home)
there may be more things... but I cant think of them off the top of my head right now... but basically they are the same thing with the same workflow. I like both, though for some reason I prefer the 2000 classic... there is no real reason for that, and I am probably the only person on the forum who does.
check here for more info and interesting stuff
http://www.mpc2000xl.com/