If the KUC file is proper, it just works when using the romtype trick, when I try it at least 
I used also an IDE with KUC extension. What do you mean with "it doesn't boot"? turboR with IDE boots fine with me and it should...
Maybe you have right about boot. Maybe it boots, but it drops me at basic prompt.
I don't know what must put on IDE dsk image to boot DOS or Nextor.
So, from basic prompt, I can't flash the kuc extension!!!
Can you give me some directions for that?
P.S. The kuc.rom file is proper for sure, but didn't work with romtype trick.
Well, you do the same thing as you do when you have a real IDE: put MSX-DOS2 or Nextor on the first partition Via a disk in the floppy drive that contains MSX-DOS2 (or Nextor) and just copy the files in BASIC to drive A: and reboot. That is, if you have partitioned the IDE harddisk. To do that you can run IDEPAR.COM from floppy after booting with the DEL key. This is all in the manual of the Sunrise IDE.
Or use diskmanipulator if you want to take a shortcut. It can create partitioned IDE images and import files onto them.
Thank you for the help. I will try it tonight at home.
I have troubles to make a working harddisk file.
Can you send me one ready partitioned, formated and bootable?
I believe a 32MB fat12 will be enough for flashing the extension.
What are the problems you're having? I'm sure I can help out
Finally I have a working HD file 32MB with the Diskmanipulator command!
I have flashed the KUC extension and now it works as it should!
The key was the use of Diskmanipulator command.
Thanks for the help.