Copying from a 16x DVD Drive to a 12x8x32 CD-RW almost always cause errors! Help!

[ILUVBC2]

Does anyone know why everytime I try to copy a cd from my DVD drive to my CD-RW drive, I almost always get errors when going through the testing phase (which I use faithfully now). Sometimes, changing the record speed from 12x to 8x will make it work. Sometimes, I have to go down as low as 4x. I would like to really understand why this happens. That was my purpose in ordering a higher speed cd drive than the write speed on the CD recorder. Of course, this could be the problem...that the DVD drive is reading too fast for the CD burner. I would appreciate anybody having an explanation of this subject.