Good morning (2004) Sapphire,
We're still (months not years) new users of the KN6000 but in that time we've come to understand some, if not all, of the technology involved.
Without sounding like geeks when your keyboard saves a 'sequenced song' it saves it in anything upto 7 different files. One of these files is the actual sequence itself. The remainder are for panel memory, sound memory, performance pads, sound fx, etc.
It sounds as if the 2600 will not accept the original APC format from whatever 'board it was originally recorded from. This has been a problem for us in that we can send a piece of music to friends with a 7000 but cannot play back their pieces because either they're using a rhythm the 6000 doesn't have or the voices used aren't installed even though we have the 6000's expansion board installed.
At the end of the day it show's that, at times, not all Technics 'boards like talking to each other. Sounds a bit like to UK or US government?
Have a peaceful new year,
Mark & Michie