If you install Mavericks, or in your case migrate from an old computer running Snow Leopard (or an earlier version of Mac OS X) to one using Mavericks, some of your software that was designed to run on older computers may not function in the new OS. See this article -
In particular -
If you see a message indicating that you can't use "this version" of an app, contact the software's vendor or visit their website to see if a later, compatible version of the app is available. If you purchased the software from the Mac App Store, use Software Update to see if an updated version is available there.
During installation, OS X moves known-incompatible software to a folder named "Incompatible Software" at the top level of the startup drive. If this folder is present on your Mac, see what applications are in it, then check for available updates. To obtain a newer version of an Apple app, check the Mac App Store, or visit the Apple Store website.
Regarding installing an older operating system on your new iMac, Apple does not support doing this, as described in this article -
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