So checking in on this thread, where did the OP end up? I bought the a6400 with the Fantasea housing and flat port for the 16-59 kit lens; I attach the AOI uwl-90f wide angle to it. My impressions: having shot an RX100 mark 1 in a tiny Recsea housing for a long time I find this new kit really heavy topside (though only slightly negative below), maybe too heavy (more in that later), but the picture and video quality are very very good. I was particularly impressed with the quality of the video using the camera’s Underwater auto white balance setting. In fact I was shocked at how good and how realistic the video was right out of the camera. Stills were also excellent and I was able to fire multiple shots quickly with my two YS-D2s without having to wait at all (flash comp set as low is possible to -3.0). So I would recommend the a6400 and Fantasea housing a lot although unfortunately the latter has been out of stock everywhere for a while.