I loved Megaman X. And one of the reasons for that is that it came with some of the most awesome tunes ever produced for a video game. As always, a fitting music can literally transcend a game, just like Star Wars would have never been Star Wars with muzac.
So I was massaging my memories if I may say and going another round of nostalgia. I went looking for the original themes, I saw those links for some covers, and decided to try them. Sadly, I soon realized that there were many people attempting, trying, but failing at making a proper cover of those awesome themes, either because they're just too out of tune, or lose the rhythm at some point, or have a synth plane that actually kills the guitar and even may make a mess of the combined layers.
Eventually, the simplest take at it may be the most successful.
But there is one guy who can actually do it relatively right, in tune, with a 99.9999 % perfect rhythm, so let's not be shy of giving him a good score. Below, you'll get to hear the original SNES theme, and then the cover, by zerosquadron.
He added his own touch but it just sounds like j-rock, it's neat.
PS: elizero17's cover of the intro stage theme is also promising, but not perfect (especially regarding the rhythm during the first dozen seconds). I'd say don't listen to her cover if you don't want to spoil your pleasure. I suggest listening to it later, because it is worth it nevertheless!