I bought the DX-500G with YS-90 Auto, wide angle wet-mate lens adaptor, and took just a few photos with it during one dive on the Big Island. Unfortunately I could not take more as I was overwhelmed with my closed circuit rebreather class and decided to leave the camera topside for the duration when I was on Oahu.
There are some issues. First, there was no DX-5000G pattern for the velcro strobe cover material included with the YS-90, although there were patterns included for other camera housings. I made one, but decided it was inadequate. Still, you need a small hole in the flash cover so that it will trigger the slave through the fiber optic cable. My recommendation is to forget messing with the velcro and use electrical tape with a small cut hole strategically placed on both the camera inside and the strobe outside, and then use the fiber optic cable attachment as normal directly above the alligned holes. You will notice a major shadow if you try to use the built-in flash with the wide angle lens attached.
Second, forget about keeping the strobe on the tray when shooting. Just way too much backscatter. As a standard underwater technique, you need to hold it away and angled, unless you are ridiculously close and there are no particles in the water. You will see that the light colored sand stirred up in the water column by beginner divers exacerbated the backscatter here. Photo used highest compressed resolution, taken with wide angle lens, YS-90 (don't remember the f-stop) off Honaunau on the Big Island of Hawaii.
Obviously my skills in this one leave something to be desired, but I was not doing artwork here. I do not like the Sea and Sea's hot strobe temperature for people shots. My Ikelite substrobe would be much more warming for faces.
I noticed no color abheration with the camera and no evident distortion with the wide angle lens.
http://nektonmedia.com/Dec-2004-Kona-003.jpg