help finding a book

Factual Questions
1

I read this book about 10-15 years ago. I think it was the first in a triligy. It started in the future, but the group of people in the story went back in time a few million years. In the past, the earth was ruled by some aliens who wore necklaces that gave them psychic powers. The necklaces could be worn by the humans also, but the one the aliens gave the humans were different and allowed the aliens to control them.

Two questions:
Anybody know what the book is?
Is it worth tracking it and the rest of the triligy down?

2
  1. The Many-Colored Land
  2. The Golden Torc
  3. The Nonborn King
  4. The Adversary

There are also continuations of the original series:
The Surveillance and The Metaconcert - details the rise of the psi-powers and contact by aliens.

and

Jack the Bodiless, Diamond Mask, Magnificat - the story of the Milieu saints and the Adversary.

I loved them all and would recommend them. The plots are a little complex, so don’t wait too long before reading the next in the series.