I've looked in the User's Guide for the WK-1800, but I can't find any reference to a "1-2-3" file type. Can you explain what that is?
The User's Guide indicates that you can use the keyboard's onboard functions to load accompaniment files made for Technics or Roland keyboards and convert them into user rhythms for the WK-1800. It sounds like the files must be loaded via the keyboard's floppy disk drive to do that.
The User's Guide also indicates that you can use standard MIDI files to play songs on the keyboard, so any MIDI editor, DAW, or other software that lets you edit MIDI tracks and export them to a type 0 MIDI file should work, but you might want to edit the data so the song uses only Bank Select and Program Change numbers for tones which are available on the keyboard. I didn't look at the tone list, but most 16-channel multi-timbral keyboards of this type have tones or voices (whatever the manufacturer calls them) that can be used to play back GM1 (General MIDI Level 1) data-- often called simply GM-- in which case the keyboard should automatically use an appropriate tone for each GM1 Program Change number. Therefore any type 0 MIDI song files which are limited to the GM soundset, or which have been converted/edited to use the GM soundset, should work.
As for tones or voices, I don't think you can load new sound samples to use for new tones, only user tone files that have been saved in whatever format the keyboard uses. A user tone file should contain data which selects a given tone on the keyboard and then sets various parameters that modify the sound of the selected tone. You should be able to use user tone files which other WK-1800, WK-1630, or WK-1600 owners have created, but I doubt whether you can use files from non-Casio keyboards.
