I would highly recommend using
DVDxDV, which I wrote, to rip the video back from the DVD. I've spent years ensuring that you are going to get the cleanest most accurate digital copy of what is on that DVD. It's far better than what your TV monitor is going to show you. Create a bunch of test patterns such as Color Bars and a grey scale ramp, and then run these patterns through your workflow. Rip the video back from the VIDEO_TS created by DVD SP with
DVDxDV. Use the format command instead of the burn command, so you don't a bunch of wasted DVD blanks. This will save you a huge amount of time. If your test patterns are off, modify your workflow until you get the patterns to match in FCP. I created a
youtube video on this.