I have searched all the official documentations, but there is not a single word says that H6 could support MMR via PCoIP on windows 8.
What's the deal?
I don't think it supports per this link - https://pubs.vmware.com/horizon-view-60/topic/com.vmware.ICbase/PDF/horizon-view-60-architecture-pla...
Refer page 20.
I don't know the exact difference but just because they are Desktop OS it is not necessary it should work. I remember windows 2012 was not supported with view 5.2 but Windows 2008 was supported. Not all Windows OS are same.