However I don’t remember the GPL being mentioned anywhere when I had my MPC X. I sold it recently because of not having any money. But I hope to own one again in the future. If I ever do have one again I will probably have a closer look at what it says about the GPL, and then try and get a copy of all of the open source portions of the firmware directly from Akai.
Just as an aside, you probably (and hopefully) don't need to have the unit to download the manual—which is where the licenses are likely mentioned. Though this one seems to direct the user to Akai's site.
https://niklasnisbeth.gitlab.io/mpc-internals/
However I don’t remember the GPL being mentioned anywhere when I had my MPC X. I sold it recently because of not having any money. But I hope to own one again in the future. If I ever do have one again I will probably have a closer look at what it says about the GPL, and then try and get a copy of all of the open source portions of the firmware directly from Akai.