First of all let me explain that MIDI means Musical Instruments Digital Interface. It is a digital code or language for storing musical information in digital format (Music Data) or communicating between two or more digital music workstation/instrument (i.e. sending or receiving musical data from one digital musical instrument/computer to any other digital musical instrument/computer).
It was initially designed to carry or store only the basic Musical Note information with controller messages such as velocity, after touch, pitch bender etc. along with tempo and channel information.
But later it was enhanced with other messages such as system exclusive and Midi time code (MTC) etc.
But it does not contain any audio data.
In a keyboard there are two sections viz:
1. Midi section
2. Sound generator section.
1. When you play a keyboard and press a key/Note, the Midi section generates and sends a digitally encoded musical information (called MIDI DATA) containing the note information and other parameters (such as velocity, expression etc.) to the sound generator section, which decodes the information and generates the sound as per the instructions in MIDI DATA.
2. The sound generator section is the sound module which can either synthesize or trigger a wave sample (pre-stored sound in ROM chip in wave format) to generate a sound upon receiving instruction in digital format (MIDI DATA) from midi section.
Now it is clear that if you have a midi port on you instrument, it can only send or receive midi data and not the audio/sound as it is not present in the midi data.
Hence you can transfer midi information between instruments to play a sound from another instrument or so, but you cannot transmit or load the sound through midi port to other instrument.
Please note that this article is not a complete description of midi - it is just to clarify that sounds of one keyboard cannot be loaded into another keyboard using MIDI.
Note: Patch parameters are MIDI information regarding how the sound will be played (attack, decay, sustain, filter etc.). Hence you can transfer or exchange patches using Midi from one instrument to another of same genre (i.e. different models having same sound generator module inside them although having different features, such as Roland JV880, JV80, JV90; XP60, XP80; etc.).
Hope this article will be able to reflect some light on differentiation between midi and sound stored in a keyboard or musical instrument.
I am quite busy these days so keep patient as I will keep posting accordingly.