Just FYI I found this answer to my question on the Cow:
"Re: Highest Quality DVD export using FCPX and possibly Compressor
by Jeff Kirkland on Jan 15, 2013 at 11:19:14 am
I've always found FCPX's DVD output to be pretty good but Final Cut's export is very much baked in - if you need to tweak, it's time to send it through to Compressor. And of course, you can save your Compressor settings back as an FCPX preset and use that next time.
Jeff Kirkland | Video Producer | Southern Creative Media | Melbourne Australia"