Hi and a warm welcome to the Nexstar forum. The 4se and the 5se share the same mount. The 6se and the 8se share the same mount which is sturdier than the one used by the 4 and 5.
The mount for the 4 and 5 will take the 6se, indeed some 4 and 5se owners have up graded to the 6se and placed it on their 4 or 5se mounts. I don't think it would support the 8se however.
I am sure other, more experienced members will be along soon to advise you further. Hope this is of some help to you.

Peter.