What is intellect-consciousness and why is it different from intellect itself?
This is just bad translation. "Consciousness" is the common word for vijnana. A better translation of vijnana is "(subjective) experience". Meaning, you see something => you recognize it => you make sense of it => you experience it.

"Intellect" is how they usually translate manas or mind.

So "Intellect-consciousness" or mano-vijnana, is therefore the subjective experience of what's going on one's own mind. It's when you "see" what you're thinking about etc. I think it's called re-representation in modern cognitive science.

It does not require a higher mind or anything like that. Based on my meditation experience, it works as a cycle. Normally the input from sense organs goes to memory to find matching associations, this is how recognition happens, the basis of vijnana. With manovijnana, instead of the sensory organs, our attention grabs data from short term memory, finds matches in long term memory, puts that back in short term memory - voila, manovijnana.