I echo juaudio and encourage you to read the Absolute Sound from one or two back issues ago because the review of the NS999ES was pretty much an endorsement of the S9000ES. The latter is an outstanding SACD (stereo only) and, surprisingly, a phenomenonal redbook CD player. Unfortunately, it's only an moderate performing DVD player. However, you'll read on audioreview.com high praise for it as a DVD player. I was fortunate enough to come across a S9000ES this past spring as a demo/close-out and got a great deal so I wish you well in finding a used one. I use my S9000ES for redbook CDs and SACD but I use a Denon DVD player for my video.
Deciding between the two Sonys depends on your needs. If you want an introduction to stereo SACD and an outstanding redbook CD (which you likely have many of), the S9000ES is the way to go. However, if you want multichannel SACD and outstanding DVD video, you'll get a slightly compromised package in the NS999ES.
As a wise one pointed out to me, "There are no perfect answers in life, just better or worse options." You might want to explore other options depending on your needs.