Kabeja does not support the shx fontfiles. To use shx fonts you could convert these fonts to SVG fonts. Then you can setup Kabeja to use these fonts instead of the shx fonts.
If you use AutoCAD from Autodesk it is quite easy to setup the fonts. On the install-cd of AutoCAD you will find all shx fonts as TTF fonts and these fonts can be converted to SVG fonts by using the ttf2svg converter of the Batik-project.
There are some programs, which can convert shx fonts to ttf (google: shx2ttf). So you can use other fonts too.
You must have all TTF fonts inside a directory, be sure that the filenames of the shx and ttf files are the same. Go to the Kabje root directory and use the converting tool from ant:
ant -f font.xml -Dfont.source=C:\path\to\the\ttffonts
or with without ant, create a directory "fonts" and use:
java -cp lib\kabeja-svg-0.x.jar;lib\batik.jar org.kabeja.batik.tools.FontImport C:\path\to\ttffont fonts conf\font.properties
All TTF fonts will now converted and stored to "dist\fonts" directory of your Kabeja installation. The converter will create a mapping file "conf/fonts.properties". This mapping file is important, Kabeja will lookup here. So you need the referenced fonts of your DXF drawing as SVG-font and setup inside the mapping file, otherwise Kabeja ignores the font.
All fonts are referenced to fonts files of the "fonts" directory, but you can embed the SVG fonts inside your SVG file. See the Processing page (pipeline embed).
If no font is set by the drawing, then Kabeja will ignore the default font. This can be done by a XSL-Stylesheet.