Medium = Message. This is a 'type' identity. The message or content of a particular piece of media is always another medium. A corollary to this could be that we are always extending our extensions, since McLuhan also defines "media" to be an extension of ourselves.
Language = Medium. Also a 'type' identity. This statement I see as an elaboration on McLuhan's discussion of light. Language, grooming, and fire I believe are some very early human media. I think if we were to really get down to it, I would say that we ourselves are extensions or physio-linguistic legacies and prosthetes of each other.
Hot media: a chimpanzee grooms her daughter.
Cold media: her daughter grunts, coos and swats back at her mother.
I'm pretty sure McLuhan mentions the fact that media cools and heats up depending on the generation or individual that re-interprets it. The temperature changes because strategies for appropriate interaction with the world changes. Actually both of those statements are different ways of saying the same thing.
Ultimately I am of the mind that this process of prosthetics and amputation of our extensions is the essence of human drama. Also, I would say that the reincarnation/samsara story is a metaphor or explanation (redundant?) for this process. (of course it's redundant; you've done this a squillion times already!)
I would also go on to say that these extensions of ourselves are exactly the antithesis of material pleasure, because if you are extending something you're not experiencing it. So:
Medium != Present
Reality, as we tend to think about it, being a phenomenon (albeit an immersive one) described or defined by its emergent properties and its overarching stories/metaphors/"Laws" is just a concept. Actually it's a very abstract, sophisticated concept. Composite reality in terms of "what-is-happening" is in truth immediate. (note the etymological presence of the very word "MEDIA" in that one!) Another way to put it is that it is ineffable, unable to be uttered. Unable to be extended.
However, human culture is incredibly good at extending itself. To quote Mr. Watts "we are menu eaters, we eat the menu instead of the food".