I currently use a Sony HDR-HC3 with a Gates Housing and NiteRider Lights.
I only use a pair of 10 watt HIDs, and I am finding that within the caverns
more light is required. Not neccessarily on the housing itself, but through support divers who carry extra lighting and position themselves ahead of me.
Through the use of underwater communications (OTS equipment) directing
the support divers with their lighting is paramount to good video.
It is expensive, perhaps $12K for the camera, housing, and three pairs of lights where two pair are carried by two support divers, add more for the communication system but the result, if exectuted correctly are spectacular.
Do not be shy, take lots of footage. You can always crop out what you like and throw away the rest.