Thanks Steve and Domin !
I haven't yet had a chance to try your suggestions but, I will so today (now - Australian daylight time

) and report back.
Thankfully, the 861v6 itself must be ok; I just tried to hook up my 800v4 as well to MConfig via same cabling (as a means of diagnosis) and the exact same symptom - 800v4 would not connect/recognise either. (Ie, I was sweating bullets thinking maybe there was a problem with the RS232 on the 861v6).
I hope there's a simple fix for all this.
I've toyed with thoughts of just buying an old RS232 Windows XP laptop but, even on eBay these are still hundreds of dollars, and I remember I did this years ago and the thing didn't work on arrival! Bit of a slippery slope..
Andrew