Islam had been spreading through domains but it was through their example of mystics, preachers and traders that it finally reached China. In China their already existed Zorastrianism, Judaism, Buddhism and Christianity and they coexisted rather well. The Arab attempts to conquer the region took well over a century. Eventually, the region began to accept the Persian culture and people began to learn Arabic. They did not fully accept the religion but developed an orthodoxy of it.
It is important to understand that Islam spread through persuasion and enticement instead of war and propaganda. Because it was able to remould the culture of the people, it was a successful religion in that it spread easily throughout the lands with little fuss. Once it was developed in Asia, the mystical piety that was established was very enthusiastic and was expressed in music, poetry and dance.
It seems to me that Islam was a fairly peaceful religion, wanting to be accepted and determined on being accepted, but doing so in a way that was not coercive. They wanted to be freely adopted by the people, almost convincing them that it was their choice. This, clearly, was very important to their acceptance and their ability to survive throughout the ages.
