The very mechanisms of microevolution are different from macroevolution.
No they are not. The whole micro/macro thing is creationist piffle. Evolution is evolution, there is no micro or macro.
In the former, phenotypic differences are achieved by shuffling genes around in the existing gene pool. For macroevolution to occur, beneficial mutations are required.
I don't see a significant difference between "shuffling around genes" and beneficial mutations.
You seem to accept that what you call 'microevolution' happens. I'll use these terms if it makes it clearer for you. Ok, so if a population of a particular animal is dispersed into a few smaller groups that are isolated from each other, is it acceptable that 'microevolution' will still occur within these groups? Lets say yes for now, is it then reasonable to say that in the different groups, different genetic alterations or mutations will take place, and of those, different ones will be naturally selected according to the specific environment that each group lives in? Imagine this happenning over and over again, over millions of years. The separate groups keep having these little bits of 'microevolution' until they have changed enough that are not reproductively compatible with the other groups anymore, or to put it simply, they can't get it on. Well, they can try but they won't be able to produce any offspring. So what's left is a few groups of animals that may have many similarities, but enough differences that they cannot interbreed. Therefore they are now different species. This would be what you call 'macroevolution'. It's not a single big step, it's just a series of little steps that end up going off in a particular direction, achieving a unique result.
Like, I cannot imagine my pet cat 'Jeb' would have much success mating with an African Lion, even though they're both feline!
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