Hi Dave,
I had built the original version using the Java 1.8 compiler. I should have recognized that in 1.8 Oracle updated the class file format. Trying to execute class files built with 1.8 with the default target of 1.8 would give you an error (which you saw) when trying to run on 1.7. Fortunately there is a switch to the compiler that sets the target. I set that to 1.7 so that both 1.7 and 1.8 can execute the class files.
So, yes, the class files have the version they are targeted for in the file and that is the error you saw. Fortunately in real life I work with these kinds of systems so I was able to recognize what was going on.
I suspect the auto router isn't multi-threaded so you might not see much speed improvement. That would be a good project. I usually just let it go in the corner until it has done multiple passes without much improvement.
I am working on a set of boards, mainly for my education. For the backplane I wrote a script to generate the traces between the sockets because of the regularity. I did use the auto router for the miscellaneous circuitry.
Happy routing! Michael