I'm stuck on shard X5... can someone provide me with an answer to this hint: is the solution symmetric about the diagonal from the top-left to the bottom-right? I've been working under this assumption but I've had so little success I'm beginning to have doubts.
Wow, finally solved it. Actually even though I was only searching for symmetric solutions, the solution I ended up with is not symmetric... ridiculously difficult puzzle.
With that I 100%'d the game, I think. Besides unlocking the locked portion of the outro sequence, are there any other secrets I should be looking for after completing all the bonus X-levels?