6 floats in total is 1.1 kg of buoyancy, which seems like a lot. Just take two floats (for symmetry) off and see if it still floats. If you want to be scientific about use a luggage scale to weigh the rig in water, just need a long enough cord so you don't immerse the scale. You could even do it at home in fresh water with care. there will be a small change between the two, the magnitude varying with the volume displaced by the housing, but getting it 100-200 grams negative in fresh should ensure it won't be positive in salt water.
This weekend I weighed my setup in a rinse tank. So it was fresh water but I think it's only 1-2% different in sea water(?) I put together my 5Dmk4 in Nauticam housing, 100mm macro lens, macro port, SMC on flip adapter, iTorch Pro6 spotter light, two Inon Z220 strobes, two ULCS clamps, 45 degree viewfinder. That weighed 1.4kg according to my luggage scale. I need to weigh it with the dome port.
Todd Winner said he has a similar rig that is buoyant two of the Nauticam arms (72218 70x300mm x2 = 1340g buoyancy.) That's probably what I'll go with. I have the ULCS metal floaty arms now but they don't do much. The Inon SS arms with the floats that fit won't do much for me, either.