Well, I have done a bit of research on this one and the following appears to be the situation:-
- From a software viewpoint, both use the same software and both can be updated to the latest version of 16.2
- From a hardware standpoint, the Mark III does have the addition of the PC input which would require quite a lot of changes to create a Mark III from a Mark II
You may find some advantage by having a software update, if your version is a very early one, otherwise I suggest you stay with what you have or do a trade-in if you can, if the PC input feature is important to you.