Ken,
These are not easy questions. I would say that the ACI600 is a richer sound while the EX separates are perhaps a bit tighter and more dynamic. There is also a liquid quality to the ACI600 that EX might not quite capture. The EX separates have the true dual mono amplifier so the bass definition and ‘slam’ is going to be maximized here.
Comparisons hold true for the EX integrated with a slightly softer sound than EX seperates but similar resolution to the other products, not quite the liquid character of the ACI600 nor the ‘slam’ of the EX separates. In any case these are exceptional products and performance and feature set for each of the price and product categories. Can’t go wrong with any of them!