And as a separate update, I installed the Dirac plugin and unfortunately the Foobar VST host is too buggy to allow the Dirac calibration software to work with the plugin.
I did manage to get around this by installing a DAW (reaper) and doing the calibration while using the DAW as the VST host. Once you have created the filter, you can again enable the foobar VST host and luckily the calibration software is able to transfer the now calculated filters to it.