Rog, It's just like connecting two different keyboards together via a MIDI cable so that you can play both keyboard's sounds, from 1 keyboard. The SMAC had all the sounds, styles etc. of the KN1200 but was housed in small module without the actual keyboard. So, it needs to be totally controlled from an external keyboard, or controller - for example a PC executing a MIDI file.
The controlling keyboard can be just a 'dumb' keyboard with a MIDI output, or any other arranger instrument with a MIDI output. These devices or 'Expanders', which were made by all the major manufacturers, could be daisy chained via MIDI connections to produce the the sounds etc. of the arranger keyboards, on which they were based. They were naturally cheaper than the instrument on which they were based and only required the addition of a 'Dumb' MIDI keyboard to allow you to produce sounds etc. from a range of expanders, if you so wished.
I still have one which was manufactured by Kawai, tucked away in a cupboard...........
So basically, they allow guys like Mike and Giovanni to produce all the sounds of a KN1200 - while playing their MIDI accordions - in addition to the accordions own sounds......... Get it ??
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Willum
After silence, that which comes nearest to expressing the inexpressible is Music.
Aldous Huxley
( especially when the music is played on a KN7000....)