As far as I know, the Ci model is available in the USA but not available in Australia where I am based. The Ci designation means "Customer Installer" These models have some extra features that make them suitable to integrate with customer installs.For example automated control via ip or serial interfaces,but there is no reason that the "normal" consumer can't use them too.Some could say it is a higher end model but there is no difference in sound quality in this regard as far as I know.The above info I sourced off the web and also have been in touch with Denon here in Australia.