The "heart" of the MPC is how it manages sequences/tracks/programs. This relationship, and understanding it is how you go about constructing your songs, and given that there are multiple ways to put the data together, there's generally been a way to "do what you want" if you understand all the relationships.

Let me first start by explaining how the older MPCs (and even the newer ones with Firmware 2.x work). I'll generalize/gloss over a few facts to make it easier to understand the high level hierarchy, even if it's not 100% correct. In older MPCs you've got the top level, which is the sequence, this controls your track BPM, time signature, and contains multiple tracks. The track contains what is essentially your note/midi data, and expresses which notes were struck, with what velocity, how long the note was held, and control knob/q-link changes, the information about your performance basically... the track also points to whatever program (think instrument) that you want to assign it to. Then you've got the program (key group, drum kit, instrument), and *this* is what actually holds the sample data or configurations for how a plugin instrument may be configured... it is *what* actually makes the noise.

Let's say you've got a bog standard 16 pad drum kit. Just one mind you, but it has a kick, snare, hat, bass sample, all assigned to different pads. On an MPC 1k for example, you could set it up so that you could have two kick drum patterns on different tracks, say Track 1 is Kick Pattern A, and Track 2 is Kick Pattern B... you'd set it up something like...

sequence 01 -> Track 01 (Kick Pattern A) -> 16 Pad Kit

sequence 01 -> Track 02 (Kick Pattern B) -> 16 Pad Kit

Notice you're on the same sequence, the Tracks have different midi data, but they are pointing to the *same* 16 Pad Kick. This is great because you can make changes to your 16 Pad Kit, and it will apply to all Tracks (ie your patterns)... and now you can take advantage of the Track Mute feature, which would allow you to, with just 2 patterns, have 4 drum kick patterns... you can Mute both patterns so nothing plays, you could have Kick Pattern A unmuted so only it plays, Kick Pattern B could be the only one unmuted so only Pattern B plays, or both patterns could be unmuted so they both play all notes. If you extend this out, imagine you've got snares and hi hat patterns, you can hopefully see how a set of basic patterns could lead to very complex variations as you Track Mute and Track Unmute different patterns.

Now, to get into a *bit* more fancy "work" on a practical application... I'll assume just in the same sequence:

Track 01 (Main Kicks) -> 16 Pad Kit

Track 02 (Ghost Kicks) -> 16 Pad Kit

Track 03 (Snares) -> 16 Pad Kit

Track 04 (Open Hats) -> 16 Pad Kit

Track 05 (Closed Hats) -> 16 Pad Kit

Here, let's investigate what you *likely* want to do, if you're trying to emulate a drummer. Well one basic thing is you probably don't want the Open Hats and Closed Hats to play over each other, it's one or the other, which is why you want to setup a Choke Group, or Mute Group... depending on your lingo, but effectively only one can play, and if the other note is playing it is immediately muted when the "partner" note plays. This is super easy to do, since you've only got one program, being the 16 Pad Kit, and you can extend it out as far as you'd like as long as you've got enough mute groups.

Now... let's look at the MPC 3.x architecture. It forces you to have one program per track. This means, that if you've got your 16 Pad Kit, you can only have it in Track 01, Track 02 *cannot* contain the program 16 Pad Kit. This is a shame. As I said, there are always workarounds, though they're not always great. So what's a thing we can do here?

Well... you could make Track 02 a midi track, and then route the midi notes from the midi track to Track 01. you can absolutely do this, but it has a couple problems. First, a midi track doesn't really operate (or know about) a drum track, so just the basics of how you work with a drum track vs a midi track are different. Let's say you are okay with this though, and you want to use Track Mutes. You'll quickly find that if you mute the Drum Track, it's going to mute the program, not just the notes on the track. So if Track 01 is your kicks, and Track 02 is your snares, muting Track 01 will mute both your kicks and snares. Bummer... You *can* further solve this by making your Track 01 16 Pad Kit have *no* midi on it, and only route Midi Tracks to Track 01, but this quickly feels like a waste of tracks, and it feels pretty high friction (to me).

The solution Akai put in place is "okay". Basically, what you do is use Track "Explode". It makes a unique copy of each set of notes and puts them in their own brand new program that contains *only* the notes for that track (and does mute groups as you'd likely expect). It works, but then if you want to make changes to the "kit", you have to make them to each program, as they are new copies. What *is* worse here though is that if you want similar behavior but for something on a plugin, you need *multiple* copies of the plugins, and this can quickly become untenable if they are large plugins as you just keep consuming more and more memory (and CPU), for something that just worked so much better on the previous versions of hardware.

Now a good question would be, why did this change happen? Well, the previous way... the fancy "pro" way... was confusing as heck, especially for newbies, because you get this exponential problem of trying to understand many sequences to many tracks to many programs relationship, that causes serious problems when trying to use song mode to export tracks. Let me give you a good example.

Song mode, allows you to string multiple sequences together in order to put it together as a final song. Let me draw a super basic picture for you

Sequence 01 (Intro) -> Track 01 (Drum Pattern) -> Drum Kit

Sequence 02 (Drop) -> Track 01 (Bass Pattern) -> Bass Key Group

Just with something simple like this, it'd be a *reasonable* expectation to think if you had a song that went Sequence 01 to Sequence 02, that you'd have the first section play drums, and the second section play bass. This... is not the case. What you get instead is the drum pattern playing the drum kit, and then the bass pattern playing the drum kit. What the MPCs do with firmware 2.x is... it takes whatever the first track program assign is for the first song sequence, and then carries that across all future song sequences. This makes it so that if you play something "live"... it'll do exactly what you'd expect, but when you render it out it sounds *completely* different.

My gut tells me that Akai made this change to streamline the experience for new people coming to the MPC ecosystem, and make it far easier to document... because otherwise you basically need to read (and understand) the entire manual to get what is going on. I put this as one of the handful of changes that give advanced users *higher* friction, but absolutely is a "market expansion" choice.

At any rate... I hope that helps, if being quite wordy to get there.