Tream, I have a feeling the problem is hardware related. Perhaps your burner can't make discs readable by the Dreamcast, or your Dreamcast can't read CD-Rs anymore. The only way to be sure would be to try burning a disc on a different computer, or trying the discs you've already burned in another Dreamcast.
Honestly, there's not really any way for a CDI to be "wrong", to my knowledge. When you burn in "RAW" mode, it's basically just dumping the contents of one CD onto another one, without worrying about the structure of the disc. The only way that could fail is if your media is bad, your burner is strange, or your Dreamcast is defective. I don't know of any way to fix the problem other than to change one of those three things and hope for the best.
I, for one, can't use cdrecord to burn Dreamcast discs, because cdrecord does not work properly with my burner. No matter what I do, cdrecord refuses to burn the first session without a pregap, which causes LBA values to always be +2 from what they should be. I long ago gave up using cdrecord and switched to CDRWIN, because it actually works for me. (Although, only the most recent version does. The one before that didn't support my burner at all, so I was forced to transfers files to my laptop to burn anything Dreamcast-related until recently.)
succeeds to bake it to CD-R in BootDreams!.
An ASPI driver is necessary,
Because XP did not have it, I installed it.
it was easy,
However, I cannot test it because there is not DC ...
Can you send the disc to someone who has a DC? If many Japanese players have trouble creating the loader disc, maybe somebody who can create working discs can send the discs to players who need them.