However when I try to access the utility class from the command-line via

java -jar C:\saxon8\saxon8.jar -TJ font.svg Process.xsl

Unfortunately this is a common pitfall. When you use the -jar option on the command line, the classpath has no effect. You need to invoke Saxon using the longer form
java -cp c:\saxon8\saxon8.jar;c:\extClass net.sf.saxon.Transform .....
Michael Kay