dvipdfmx emits a lot of warnings and Koji suggests ps2pdf.
Thanks to Koji for the advice.
Note that on Debian, I installed the following packages
to be able to compile with ps2pdf:
fonts-takao-mincho
fonts-ipafont-nonfree-jisx0208
fonts-ipaexfont-mincho
The rest (Tutorial.lyx, Math.lyx, EmbeddedObjects.lyx, UserGuide.lyx,
Intro.lyx and Additional.lyx) are left untouched, because
still not compilable with platex