"You can swap (crossgrade) the platform or language of a single-user product to a different platform or language of the same product. Swap (crossgrade) if you've been using the product on a particular platform or language, and then change your operating system or require a different language version.
You can swap only current versions, and only if the equivalent product is available for the new language or platform."
I am thinking that the best way would be to first perform the platform swap and then upgrade to the newer version.
Read this document for more info. Order Product : Platform, Language swap (http://helpx.adobe.com/x-productkb/policy-pricing/order-product-platform-language-swap.htm l)
If you join the Creative Cloud you can download & install CS6 on either Mac, PC or both and you get regular upgrades as soon as they are available.
Save 40% on Creative Cloud subscription
Perpetual License users must obtain either Mac or PC version of the software. And you only get minimal updates. Contact Adobe regarding a cross-upgrade.
Correct me if I'm wrong, but as of 12/31/12 didn't Adobe go to a 1 version back policy on upgrades so they would not even be eligible for a cross-grade because an upgrade is no longer available.
Not sure why Preran suggests platform swap then upgrade since neither is possible in this case.
The options here are to either purchase a full version of CS6 or join the Cloud.