I am now successfully communicating on the Bus!
I have learnt that the correct response to a status request is quite logical...
MID asks RAD if it is ready
RAD replies to MID, yes I am.
So the response to C0 03 68 01 AA is 68 04 C0 02 00 AE which also keeps my test keypad alive. So once again, Dog is like a Dog with two Richards.
Both Ian's library and the previous one I was using worked beautifully. Now for the development work. 
Old library is controlling the radio via IR happily. Now to see if I can sort the variable clash with Ian's...
My grateful thanks to Ian and everyone who has contributed.