Four great elements : what is the other 2 elements? I have heard about "Mahabhutha" as 4 elements but in few occasions as 6 elements with the addition of "Akasha" &amp; "Vijñāna".

Can someone explain why there is a difference and how they connect with the other 4 elements?
Four great elements : what is the other 2 elements?

In the Nikaya Texts, there is a term called 'Cattari Mahabhutani'(four Mahabhuta). These Mahabhutani consitute Rupa. (See Sammaditthi Sutta). 

A being (human being is an instance) is defined in terms of six Dhatus. It is Cattari Mahabhutani and Akasa and Vinnana Dhatus (Caddhaturo Ayam Puriso) (See for example Bhahudhatukasuttam.) However, there are no meaningful translations of these Suttas in any language. These Suttas could be understood only by Lord Buddha's direct disciples, who listened to Lord Buddha in person. This non-understanding is the reason for the existence numerous Buddhist traditions and sects.