Hi Tony, Any Technics compatible footswitch will be OK to control Fill-Ins etc. - it's just a case of assigning the footswitch to a particular function in 'Program Menus/Control/Foot Controllers'
As far as the OS on your new PC is concerned, it doesn't really make much difference, since the KN6000 has not got a direct link (USB) to the PC. If you intend to use a MIDI link for a PC sequencer program, again it's not important as far as the KN6000 is concerned - the sequencer program would of course have to be compatible with your chosen OS.
If you just wish to connect the Audio output from the KN6000, to your PC sound card, for recording to CD, then again, the choice of OS is not really a concern.
Much as I hate to say it
it would probably be best to go for XP since Win98 and Win ME will shortly cease to be supported by Microsoft, although WIN2000 still has a bit of life yet
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Willum