Here is what I have understood in brief. I am on travel and thus not able to access all my resources.
1. Vimokkha basically means “becoming free”. When one attains Nibbana, that is the final and complete freedom. So, it refers to Nibbana.
2. Vimokkha (or Nibbana) can be attained via contemplating mainly on anicca, dukkha, or anatta and thus leading to sunnata, appanihita, animitta Vimokkha. Of course it is the same Nibbana that is reached. It is just following different ways of getting there.
3. Based on the types of individuals, eight types of individuals are indicated (attha vimokkha): Pannavimukta (those who have high wisdom), Saddhavimukta (those who have faith),etc. Again, it is the same Nibbana that is reached.
I will try to find references when I get back (or someone can post if they know). But please continue the discussion.