i find out, that the voice files are made with OKI VoicePro2 Software.
http://www.okisemi.com/english/ar204.htm

the sound chip in MK4 is build by OKI, called MSM6585.

but the software works only with Win95. i can not test it, because i dont own these old OS.

i hope the soundfiles can be edited with this software. is anybody able to try this on a Win95-system?