HI Tim: As a past partner in a Scuba Diving shop. We sold both Sea&Sea at a ratio of about 10:1 housing over Ike. Ike makes a good strobe, but the housing in my opinion is no way a nice looking, and the plastic just isn't aerodynamically pleasing. The tended to be more mechanical without the electronics built in with S&S. Also this probably represents shop bias, we dive a great deal around the world as a group and I have never seen an Ike housing on any of our trips. Upside is they will be significantly less expensive. I don't know the difference between the D40 and the D400 but it seemed like you were receiving reasonable advice.
You might consider talking with Joe Liburdi. He is retired now but is always willing to help photographers. He is 78 years old and has been diving and shooting under water since Moses Parted the Red Sea.
You can contact him at his travel site, www.joeliburdi.com I'm on my 5th digital camera, only real advice I can give on housing is buy it right the first time. Also Joe and his wife Cara wrote the Book on Sea and Sea Cameras.