I'm trying to remember this book I read back in the 90's but I suspect may be older.
Humanity gets discovered by three alien superpowers and they split humanity into three groups and take over/enslave them.
I think one empire is called the exchange and they are like a capitalist empire, one is like a machine civilisation and the third are parasitic?
They discover a being that resembles a demon on a planet and find out that the demons where actually an ancient race that visited all the planets in antiquity as they exist in all of the alien races mythologies.
Each empire then assembles a team to try to reach the demon (can't remember why) and it's a race as to who can get to it the first. I remember the demon race travel by using tesseracts and humans are marked on their fingers with different coloured bands to tell people if they are telepathic or telekinetic etc.
The book art was a guy looking at a huge block of ice in which a huge demon like creature is frozen.