As an update, I've been speaking to Octava support with regards to the feedback message. I did get a reply back from them with regards to my unit, which is an older model (at least 18 months old). It seems the feedback code for older units like mine is not consistent, there is however a software update that I'm trying to get hold of that uses their new standard.
"The feedback code- on previous versions, we had not anticipated that users would be using the feedback. We were using the feedback strictly for our internal development of a windows program ( to control the matrix) https://octavainc.com/faq.htm#RS232control
I am thinking, that if you are indeed going to write feedback code for drivers, then it makes sense to use the New code.
I have attached the latest documentation they have sent me which includes details of the feedback code. I am now trying to get a software update for my system so I can use this code.