I also like the name Sophia, but you might point out it isn't an uncommon name anymore. There are a TON of Sophia's or Sophie's right now. My oldest son's preschool class had 2 Sophie's - and it was only a class of 8 children! There are three Sophie's or Sophia's in his first grade class. Perhaps something a little more unique would be to his liking. Play upon how special your daughter will be, and how her name should reflect how special she is. A man thinks his daughter is the most wonderful creature on the planet. If you have him realize how common the name he's chosen is, and he might go for something a little more unique.
Try looking up the Social Security Administration website. You can look up the popularity of a name within any year or span of years. This will prove how common it is. Just "google" Social Securty Administration, and you should be able to find it..,