Just to finish up - this was successful. I ended up choosing MRC Simulator for the connection and then did a number of searches and replaces on the original xml to find and fix up the system names to match the correct 'Internal' connection pattern for turnouts (ITnn), routes (IR:AUTO:nnnn) and blocks (IB:AUTO:nnnn).
Thanks again for outlining so clearly the reason for the behaviour that was at the root of my issue, Dave.
Cheers
Simon
