I have a D200 in Ikelite housing with DS 125 (SINGLE OR DUAL) and underwater the rig is slightly negatively buoyant, which I prefer (unless out over a wall) as I'd rather have a dropped camera go down than up.
I have (until now) used the older 8" dome port and it gives the whole rig a "rotational" effect, where, if minimally held, the dome port wants to rotate the camera setup vertically so that the dome port is pointing up, say 60 degrees (just a guess). That rotational drive from the extra air up front in the dome port is notticable underwater, but not a big deal. I don't notice it with a flat port or 6" dome. I haven't dived with the 8" "system" so I can't say it it is the same with that system as the old 8" dome.
Ike (God rest his soul) gave the best service in the world, and I am hopeful his family will continue the same.
Steve Dingeldein, M.D.