Most Christians are not aware of the tremendous differences between the authoritative foundations of their scriptures and the Koran. They simply ignore the fact that the Bible was a compromise reached by a committee, and treat it as the authoritative word of God. They shouldn't ignore this fact, but most do.
I don't think, however, that these sorts of problems disappear once one accepts that the Koran is the direct word of God spoken to Muhammad. The problem is, language gets essentially all of its meaning from the context in which it is spoken, which means the only way one can understand the Koran is to recreate as best one can the historical context in which it was revealed. This is why it so important for Muslims to study both the Koran and the Hadith. When the Koran speaks of "the Jews" or "the Pagans", does it mean all Jews and Christians, or only the Jewish and Pagan Arab tribes that were trying to slaughter Muhammad's people. Sometimes it means one, sometimes the other, and it is very difficult to be sure which is which.
There is also the question of applying the rules implied in the Koran to new cases. Do rules about camels apply to cars? Do rules about swords apply to missiles? Muslims scholars use their intelligence as best they can to answers questions of this sort, but they often do not come to a consensus.
I've been studying the Philosophy of Language for decades, and these problems are much much bigger than most people of any religion realize. They are the main reason that no one has succeeded in building a computer that can understand ordinary language. Philosopher John Searle calls this context "the background" and every sentence gets most of its meaning from this background, and very little from what's actually on the page. This is as true of a sentence like "I'd like a steak with potatoes" as it is with any sentence in the Bible and the Koran. Consequently, even if God or Gabriel spoke directly to Muhammad, we are still left with the hugely challenging task of figuring out what the words meant at the time, and what they would mean today.
I left Christianity and became a Buddhist because of this problem of interpreting Sacred Texts. In Buddhism, we have revered texts, but no texts that can be trusted absolutely, because the truth is seen as something that cannot be expressed in words. I may have move too hastily, for I have since met many Christians and Muslims who recognize that precious as their sacred texts are, they do not absolve you from the responsibility from figuring how to apply their truths to your own life.