Unfortunately, there is no direct way to play KN6000 files on a PC.. The file components you mention are only understood by the later Technics keyboards KN6000, 6500, 7000, 2400, 2600 etc. so they will not be playable on any other software.
However, it’s not all bad news…. If you have a tape recorder, or cassette recorder, you can connect it to the line outputs of the KN6000 via appropriate leads and then record and play back the songs on the recorder. This doesn’t get around the problem of playing back on a Windows 10 PC . Although it would be possible to connect an audio recorder to a PC and then record to files on the PC, it’s a bit long winded and quality may suffer along the way…..
An alternative….If you know anyone who has a KN7000 or a KN2400 (both have Floppy Disk Drives) then it would be possible to load your wife’s songs from Floppy Disk to the KN7000 or KN2400 and using a program such as Audacity or Goldwave (PC audio recording programs) and a USB connection from keyboard to PC, to convert her songs to a format suitable for listening on a PC.
If you don’t know anyone who has a suitable keyboard to effect the transfer, if you wish, you could post a Floppy Disk containing her songs to me, together with a USB Memory stick, I’d be happy to do the transfer process for you.
If you wish to discuss this further……. My email is : email@example.com
Website : http://www.willumspages.co.uk
Richmond, North Yorkshire