ahh, cave photos .. something I can help with 
started out with housed film (nikon), then on to canon a640.
remote strobes are your friend
... I use an Ikelite adapter to go from the lower threaded rod on the doubles, to an arm system, use a 6" arm, then mounted to the strobe, then use a 3' extension, on a slave sensor, and you have the abilty to aim the strobe where you want it, and the diver holds the sensor (hopefuly pointing it at you).. works great with the black ikelite 200 strobes (i'm in the process of 'painting' my sensors so they're black also.
when not taking the photo, the strobe tucks in behind (below) the tanks, the sensor goes in the divers pocket, no entanglement risks, still nice & streamlined.
My current setup is the a640/ike housing, inon 100° wide angle (wet lens), 2 ss200's on the housing, 1 on the model's back
next trip (october) i'll play around with positioning a strobe or 2 on the floor, behind something (again the 3' extension on the cord is a big plus
now.. for some photos 
one of the last ones I did on film

similar shot, with the a640

2 divers with back mounted strobes, 1 on camera

same 2, one on left has black strobe, one on right is the orange one (soon to be sharpied black)

lots more photos here it can be slow to load sometimes, be patient.