I have Supertraining by Siff and it is hailed as a supreme book on training but isn't really the place to start out with. Probably more suitable for someone who already has a pretty good knowledge of things and wants to take it further. The book gets referenced all the time by authors so if you have the patience to get through it then you will learn plenty but like I said it can be a tough read.
Science And Practice Of Strength Training by Zatsiorski & Kraemer is often considered better by many as still has all the information but is much easier to read.
I'm guessing the other book you are referring to is Secrets of Russian Sports Fitness and Training by Michael Yessis. I don't have it so can't really comment.
Pavel Tsatsouline has written many books about Russian strength training and I own most of them but I wouldn't really recommend them. They are an interesting read but a lot of the things in Power To The People for example I don't particularly agree with. Beyond Bodybuilding is pretty good though and worth a read.
A much better book that I highly recommend is the Black Book Of Training Secrets by Christian Thibaudeau. It really is a great place to start.
Read that then get Theory and Application of Modern Strength and Power Methods by Christian Thibaudeau. It goes more thoroughly into the science of it all.
One more book I highly recommend is Modern Trends In Strength Training by Charles Poliquin. It's mainly a book about different training methods . It's set out in an easy to read format that you can easily come back to whenever you wish to apply the methods into your own training.