The Evocation Keys do not need to be experienced in full, complete clarity to establish a connection to the demon. In the early days for me, I hardly experienced anything at all (aside from amplified emotions) and I still got good results.
It took me many months of regular evocation before I was able to have meaningful conversations with the demons in ritual. This is normal. Trying too hard to hear the demon will just result in you talking to yourself.
How I hear the demons varies. When I am focused, most often, I allow them to speak through me, aloud, in my own voice. At first this likely appeared as me sitting alone in a room and talking back and forth to myself like a lunatic. Over time the experienced evolved. My body was compelled to adopt a certain style of speaking while the demon speaks, and this differs with different demons. A variation of the yogic ujjayi pranayama, which I think of as the “demon breath,” also arose naturally at one point or another. Are these “dramatic” elements necessary? Perhaps not, but I cannot argue that they do not create a profound sense of immersion into the task at hand, without conscious effort on my part.
At other times the demon will “speak” through what I perceive to be a normal thought, though the mental object will have a subtle property of “otherness” to it. There are also, of course, synchronicities and omens and dreams and such things, though going too deep down that rabbit hole is how you infinitely second-guess yourself and go insane. Enjoy them and don’t worry about it too much.
I would be wary of bouncing around between methods (often of dubious quality). There is no one way of performing magick absolutely “correctly,” but there are certain pieces that need to be there for things to work most effectively. If you compare the DoM method to, say, Koetting’s method of evocation, you will find many core components of the rituals to be shared between them, though expressed in a different way. This is why I believe magick to be both art and science. There are processes that work and those that don’t (or perhaps not as effectively), but the “aesthetics” are largely a matter of personal taste.
I will not lie to you. I have not used the enns, but most often when I hear them referenced, the context is people linking to one of the videos that you reference and claiming it to be sufficient for magick. Perhaps it is, I have not tried it, but I doubt it. People are so goddamn entitled nowadays that they cringe at the thought of magick requiring practice, persistence, and skill. You will hear many declare good magick to not work after it did not manifest their wildly unreasonable request in a matter of minutes (or perhaps days, if they are especially patient). Such people prefer to turn on a video with flashy colors and entrancing music and pretend to be a big, bad, powerful black magician. If you want this experience, go to a music festival. It will be quite enjoyable, but this is not magick.
If you want real magick, then place your trust (or at least your skeptical attention) with respected authors. It would seem that people are really beginning to capitalize on the growth of various “metaphysical” movements, and few of them will provide you with true magick that works effectively (though many would have you buy their copy-paste book or course). There is nothing wrong with peddling pretty rocks and trinkets and good vibes, but they will not provide you with real magickal change (not to disparage quality sellers of materia for witchcraft and the like).