The most concise way would to describe the similarities and differences is to say that Digital Immortality is a path into the future, whereas Transhumanism is a mindset towards the future.
Aims Of Digital Immortality MovementEdit
Aims Of TranshumanismEditThis video takes a more in depth look at what transhumanism is about. Keep in mind that transhumanism is the host of humongous amount of ideas, and individuals are going to have preferences as to what ideas they support. Transhumanists are not always going to agree among themselves, and they are not going to always agree with the digital immortality movement.
Transhumanism is very broad and doesn't seem to have too much in terms of direction. While it does have some of the same philosophies and ideas that are contained in Digital Immortality, D.I. has much more specific goals that we are trying to work towards. Also I just really like that D.I. implies indefinite lifespan.