Update: Looks like our review of the Belkin AV360 might need the weekend, or how ever long it takes for Belkin to respond to our several queries. We're pretty much done, though. We found out what Belkin meant by "scaling," too. It means you don't need to pre-set your devices for 720p input to work on the iMac. The AV360 will simply scale them down for you. Convenient.
The need for such a device comes because Apple's largest iMac, unlike its large-screen Windows counterparts, comes equipped with only a Mini DisplayPort for video input. That works great if you want to use the iMac as a second display for a MacBook, less so if you want to hook up a game console, cable box, or Blu-ray player.
As with the Kanex XD, the Belkin AV360 faces an important limit in that the iMac's screen is only designed to accept video signals from certain screen resolutions through the Mini DisplayPort.
Native 2,560x1,440 works, but Apple left off 1,920x1,080, aka 1080p. Instead, home entertainment devices will drop down to 720p to meet the iMac's next highest setting, 1,280x720. We found that game and cable box content looked fine with the Kanex, but Blu-ray discs lost some clarity at that resolution. We haven't tried the Belkin AV360 yet (look for a review soon), but we wouldn't be surprised to find the same situation there.
The differences between the Kanex XD and the Belkin AV360 are minimal. Each has a $150 recommended price tag. Belkin's device is about three times longer than its competitor (6.25 inches vs. just over 2 inches). The Kanex XD has an external power supply; the Belkin model is USB-powered.
None of those differences seem that significant. The chief differentiator may come down to scaling. Belkin says the AV360 will scale video content to fit the iMac screen. We can't say we noticed any untoward boxing with the Kanex XD, but we'll be sure to do a side-by-side when we write up the Belkin review. Look for it by the end of the week.