the .kar files from the internet are in type 1 karaoke format. I am not certain about the psr8000, but the psr630/730 only displays lyrics for type 0 karaoke. So it's not enough to change the extension to .mid, you must convert the type 1 file to type 0. There are several programs that can do this, that can be found on the internet. The simplest one I found is called "one2nul", if you run a search for this filename on altavista, it should give you a site to get it from. I hope this will help,
regards,
msz