Man, I was one of the first to switch from the mpc2Kxl to a MPC4K, almost 2 years ago to the day. I had to sell a bunch of stuff (MPC2KXL, ASRX and RM1x) to buy the machine and let me tell you... it was ALL WORTH IT. You will have ZERO regrets.
Even back then when the OS was full of bugs it was still miles beyond the MPC2Kxl and all the gear I sold. Basically, if you have a computer set up with the MPC4K it's probably the best setup one could possibly imagine.
(if you dig hardware sequencing). I found that using the MPC4K as the master sequencer and using VST instruments, my mo-phat, Nord and my sp12 as midi modules/synths was the best setup.
If you can imagine this scenario: take a drum break on the computer use recylce to chop it up and create the Akai program file. Drag and drop that into Ak.sys, it loads up in as a sequence/program on the MPC in a fraction of a second. Screw around in SEQ EDIT to re-program the break. Go to the Drum mixer (new in 1.51 OS -- which is DA SH*T !!!) to add effects or vary the velocity of each pad/part. If there's a specific effect that I want that's not available on the MPC4K, I just go to Ak.sys, click the sample I want ; edit in SoundForge or Wavelab, save it and it's atomatically updated on the MPC4K (via Ak.sys). After the break is nice and unique, screw aroud with the q-link to give it some filter effects. Add my other tracks (synths, pads etc.). Then utimately record into CUbase OR record each sequnece as a loop and drop them into ACID 4 to do some really wicked arrangements (this what I do nowadays -- and save cubase for mixdown/mastering).
All this takes very little time because everything is integrated (thanks to Midi and Ak.sys). You see what I'm sayin? THIS is the beauty of the MPC4k. It's the best machine I have ever owned and with thenew rock solid 1.51 OS, nothing can even come close (hardware wise)
Longwinded but you see my point as to why you will have NO regrets about getting the MPC4k (and you won't either).
Respect!
"hey you with the glasses, hey you with the panties, hey you with the big head, hey you with the suit on, come here fish face... when i'm on stage treat me like 3rd base" -- kool keith (ultra basement tapes)