To start off with let me say I have never used nor had 1st hand experience with the DC600. What I am about to write is based on my experience with my 500 model and then studying the pictures on the Sealife website for the 600.
The 500 for me was a great intro camera but one of the first things I began to notice was that the colors in the photos (and I used a strobe) were flat. There is very little "pop" to the colors that the camera captures. While the colors are definately there the rendition to me is undersaturated to a large degree. This picture is one I took in March (I began to take UW photos this year for the 1st time) with a strobe. There is very little color in the color or the area around it that the camera caught.

This is not just one incidence. It is much easier to see with a series of photos all at once. If you go to my album from March which is almost exclusively the 500 model photos and dont look at a single photo but rather the album view with all the thumbnails you can see the lack of color. http://good-times.webshots.com/album/557964721fNfxRD
I soon switched to a Canon G7 to take better pics and videos and the results were certainly more colorful.

Again, go the album view where you can see thumbnails and the overall color difference is very evident. In my opinion there are alternate choices for an UW camera that would work better than the 600. Whether its a G7,640 or Olympus you might want to look around for some more sample photos to judge from. That same $1400 will buy a G7, Ikelite housing and a DS51 strobe and I am sure a similar setup from other manufacturers.