I have loaded in a .MID file that I downloaded from the Internet and none of the sounds are correct.
It is likely that those files are intended for a GM instrument. The important thing to understand is that General MIDI has nothing to do with Standard MIDI Files. A .MID file is simply a sequence file saved in a standard format. But General MIDI is a term which refers to an instrument having a specific set of sounds, located at specific program numbers, along with various other standard rules such as drum note layout, etc.
If you have a K2661, there is a complete GM sound set on board. It is possible that your sequence does not automatically switch the instrument into GM mode. This can be done manually on the MAST2 page. You can also edit the song and set the GM parameter to ON.
The K2600 is not a GM instrument "out of the box". However, there are two solutions to this issue.
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