I hope that this image can give a new interpretation to the problem, that may be a bit more clear that other non-graphical interpretations. I have created a line expressing different levels of being 'into it', where further to the left is less into it and further to the right is more into it. Not here acts as an 'operator' giving you all the parts of the line that are not part of the original statement (really into it is a subset of 'into it') and 'not into it' is anything that is not 'into it', the same holds for 'not really into it' - which is shown graphically with the blue line - signifies anything that it not 'really into it' and therefore much less extreme than 'really not into it' which is an extremised version of the already more extreme not 'into it'.
Note that although saying 'not really into it' when you are 'really not into it' is technically correct, it would still be considered quite an understatement. 'Not really into it' is more generally used to describe lower levels of being into it that fall somehwere between 'into it' and 'not into it', this because saying 'not into it' would be too negative for the speakers need (it excludes all of 'into it') and 'not into it' would be too extreme too (because it excludes all of 'into it')
I would not be certain which is appropriate in your case since I am not well versed in either Ancient Egyptian or the national football (soccer) league, however for ancient egyptian I would say "I really don't know anything about that" and for the national soccer league I would say "I don't really know anything about that".
As you might have noticed from my lexicon, I am rather technically inclined and like putting concepts into easily categorizable boxes, if you prefer to understand language solely on an intuitive level then I encourage that you ignore this answer and don't bother too much trying to understand my jargon.