"Is there any significant difference in the quality of perceived signal. If no then why have two on the AR9000 and if yes then presumably the AR9000 is significantly better. I am have trouble understanding the logic used in the variants since it is impressed upon us as the buying public that there is signal diversity; if so then surely the AR8000 is a poorer brother to the AR9000 (or any type using a twin aerial arrangement on the main receiver"

Your answer doesn't address the question. Perhaps it was badly put but if the 8000 is OK then why the 9000 since we have three aerials its ability to "see" most of the RF signal is almost as good. Not sure if I can attach the logger to the 8000 but I have had one and frankly its not worth the trouble. I do sometimes record the losses etc on a flight recorder which is a little more useful as you then you know when it happened. I am in the throws of buying another receiver but dont want a 9 channel as with an aerobatic model 6 or 7 is sufficient but I want to know if the 9000 is worth the extra pounds over the 8000 (Three against four aerials or is it anything else that I am missing here?)