I'll look for the ctr decryptor problem.
I do not have any keyX, and i thing MT or GW don't either. They just hardcode a customized key i think, that's what makes their saves unreadable in real cardriges.
I actually didn't touch the function that generates the key, so on sysnands below 6.x it is probably bad generated. So, games you start in rxMode will just work on rxMode. That's the problem of the compatibility.
If you are wondering, i do not own the real keyX or the GW/MT one.
The only solution would be savedatafiler or an opensource homebrew with the same functionalities.
Also, you are forgetting i'll port the mset exploit to 6.x too. That would be good, since is the minimum firmware for 2ds and the save keys are properly generated