Is there an intuitive channel through which the higher self communicates impressions to the upper subconscious, for example, to sense a warning or to feel pangs of conscience, or is that always done through the deep subconscious?

Here again, your intuitive reach is spot on. This is happening through the deep subconscious, so the gateway from the deep subconscious to the upper levels of the mind is inadequate in most cases to provide meaningful information. Mostly what is happening is there is a meager intuitive awareness that there might be a problem and this is accompanied by an emotional reaction in the body generated by the deep subconscious in response to signaling from the higher self the person is going to be in trouble. So that slight intuitive awareness there is something important connected to a plan or a thought or an activity underway must be reinforced by a strong inner feeling, an emotion of some kind, and that comes from the body courtesy of the deep subconscious stimulating an emotional reaction. So the latter is not intuitive per se, it is the combination of a bodily response generated directly through the ability of the deep subconscious to impinge on bodily physiologic function in the firing of nerves and generating hormones, and so on. The actual information about the meaning of the emotion is often lost because the intuitive connection is dim. This is the reason why states of chronic anxiety, even of great severity, are often a total mystery to the sufferer because they are getting no information content whatsoever about the dilemma being perceived by the deep subconscious, which suffers greatly from the burden it is carrying and has such a poor ability to sound the alarm in anything other than a vague fashion through bodily feelings of emotion that are a generalized phenomenon and could arise from a myriad of causes, and often presumed to be just a bodily dysregulation with a biochemical basis or even a genetic predisposition for dysfunction. The true meaning is obscured because the function itself is faulty and unable to solve the mystery on its own.