Thanks everyone for replies.
Afterall, I decided to go for Ikelite Housing and DS-125 Strobe and sold YS-110. Ikelite's DS-125 is a fantastic strobe and its only downside is its size and weight which is kinda' pain in the butt when flying overseas. Despite that, no issues - the battery lasts for at least whole dive day, has TTL, and it's all I need.
The housing is a separate issue: it's really hard to operate it with one hand - the shutter trigger is designed to be operated with your thumb - not index finger so if you'd like to hold on to some piece of rock or dead coral if the current is strong you can't hold the camera and take photos at same time. I unscrewed the handle and turned it around 180 degrees so I could hold it with my right hand and then redesigned the trigger to be able to operate it with my index finger. That helped a lot!
But I think it's time to move on and go for DSLR (I wish I did it right at the beginning).
Don't get me wrong - G9 takes good photos (some of the shots i've seen on people's Flickr are really awesome), but in my case i was able to produce the best results for objects 15 cm and bigger - unless I was photographing nudis which don't move at all so you can get close enough to them to fill the frame. I was getting very frustrated when trying to shoot a Mandarin fish in Sulawesi last year - this very shy fish didn't allow me to get too close to it, what resulted in all of my photos required cropping.
And there was much more occasions where I had to decide whether stay away and crop the photo later loosing on it's quality, or risk spooking the object when trying to get closer.
I was trying to find diopters which would allow me to INCREASE the FOCAL DISTANCE and MAGNIFICATION at same time, but the one I bought increases magnification, but shortens focal distance, which was completely useless in my case.
If you know about any of this type of lenses for Ikelite housing please let me know.
I recently upgraded my old Canon 350D to Canon 50D and bought 100mm marco lens, and it seems to be perfect set for type of photography I'd like to do - at least that's my imression when taking photos on the surface. The only problem is the cost of housings - I'll probably go for Ikelite again because it's the cheapest and because I could still use my DS-125 strobe which would reduce the costs of completing the new set.
BTW: Does anyone have any experience with Ikelite housings for 50D?
Thanks again and looking forward hearing more advices.
All the best
Tom