Cor,
Hope you are having fun (Solomon's)
, but just in case you have found time to check wetpixel, here's a ? for you and my current experience with core cell, ULCS buoyancy arms, etc.
I'm having a tough time getting my new subal ND20/D200, system more neutral. I'm also using the core cell material on ULCS in combo with ULCS buoyancy arms but I haven't found the right combo yet to make it light enough. Ryan Canon has done some calculating and is sending me different arms with more core cell foam that I hope will work. I'll let you know which combo I come up with. Right now he estimated by weighing all my items u/w that my D200/Subal system is 3 lbs negative underwater (without core cell). It seems more but even that is unwieldy for me (I recently suffered a right hand strain injury that put my right hand out of commission for a few months, so I'm very cognizant about unnecessary strain with the rigs now, especially on long bottom times, injury is no fun).
What strobes do you use with the D2X/Subal, etc?
I use the Inon D2000Ws and I think that is a large part of my problem as they seem to be more negative u/w than the Inon materials state. They are hard to position for me because of their heavy u/w weight, etc. I'd love to get rid of them but I don't know what else to get that would help me, I've been looking into various other strobes, even bigger strobes that are positive u/w, but I'm not sure they are good for macro. I'm going to be asking a lot of ?s at DEMA in a few days.
Also, Berkley White told me he has a "machinist" who could carve me a buoyancy ring for the 105 port. I know James Wiseman made a ring, but I can't do all that......
; especially recovering from injury. So I'll probably take him up on that, hopefully using the same core cell material.
Yup, take it from me, sore arms or hands from a heavy rig on numerous long dives might just be an annoyance, but if it turns into injury then it is really a drag. Here, prevention for you is much better than the cure that I have to go through now.
I'm telling retailers now and manufactures that I WISH they would make the housings/strobes, etc lighter underwater, but the answers I'm getting is that "small sells", etc. Also lots of the customers are strong guys who don't care so much about the in-water weight................
OK, just curious about what strobes you are using as part of your system that you are trying to lighten and their weight.
Thanks so much Cor (I love your photos!!) 
Best, Carol