Update for those with a similar condition - I have experimented with a different laptop and another USB null modem cable, but have exactly the same symptoms. These are not being able to fetch/save from/to the 861v4 from the Meridian Configuration Programme, despite the 861 being identified by the laptop.

Yes I can use the MSR control window and yes the port is configured correctly. I have been at this for many hours now and my wife commented this morning that I must have OCD to waste so much time on it...!

However, there is some light on the horizon. I attempted fetching with the Meridian Legacy Programme, it connected first time! And so after configuring the 861 cards, speakers, sources, etc. I am now ready to start room correction once the cinema seats arrive!

Am I missing anything using the old Legacy software?

Thank you, Simon

.