I thought by the title that you would mention the Buddha, who says:
What is the All? Simply the eye & forms, ear & sounds, nose & aromas, tongue & flavors, body & tactile sensations, intellect & ideas. This, monks, is called the All.
That is to say, the all is only the perception; the one that perceives (subject) and the perceived (object), nothing more.
A well-known concept or theory on perception, is that of The Looking-Glass Self by Charles Horton Cooley.
It is interesting, if our perception is created based on the information we collect from our environment, it means in turn that we also influence the perception of those around us.
This means that there is a feedback between all, and therefore, none can be the cause of perception, but all work together. And I refer back to Buddha; for there to be visual perception (vision) there must be something that is seen (object) and someone that sees (subject).
About media, you mention culture hegemony, and Gramsci does a very good job of developing it, however, he makes the same mistake as all Marxists; reductionism.
Just as a reciprocity between the one who perceives and the perceived is necessary for there to be perception. It's necessary that there is reciprocity between governors/rulers and the governed/people so that there is governance. Therefore, there cannot be a cultural hegemony created unilaterally.
I don't say that such hegemony does not exist, because it does, but I say that such hegemony has been created with the consensus of a large part of the population, and until they don't stop supporting such hegemony, it will remain intact.
Although the government allows propaganda to be diffused on TV, no one is ever obliged to see it, therefore, and as I said, there is feedback.
Excellent post, a lot to think about, and a lot to comment on, and for this I regret having extended myself so much. Regards!