As long as you meet the requirements of the exam, you can apply for it, and you don't have to worry about whether you have passed Band 6. The difficulty of English test is also about band 6. If you want to get a doctorate, you should make up your mind and prepare wholeheartedly.

Go to Shanda's website to learn more about the exam dynamics, and do well in the exam questions over the years. There is no problem in passing. I suggest you buy it at Baidu's Hua Hui Education Store. The materials I bought there are highly targeted and specially take exams with teachers from various institutions. I hope it will be helpful to your study.