Hi
I can't comment on the Amphibico but I faced a similar decision between the Gates and Light and Motion Bluefin HC3
I went with the LIght and Motion in the end for the following reasons. They make sense to me but may not be right for you
The Gates housing had no access to MWB (although WB adjustment was available through the assignable button and roller). I believe for the HC7 Gates now offer access to MWB but I'm not sure if they can retrofit for the HC3.
I like to be able to switch from wide angle to macro on the same dive. In order to do this with the Gates I would have needed the Fathom Super Wide port at about £2000, which also looked pretty big against the housing. The other ports were either wide angle with little or no zoom through or flat ports for macro. With the L&M the standard port allows a reasonable wide angle and also allows full zoom through including the tele macro facility on the HC3 (I also got a L&M wide angle port as part of the package that I will probably use on wreck dives where I can be reasonably sure that I only want Wide Angle)
I wanted a very compact light system. Most of my videoing is done in warm clear water (Red Sea, Indian Ocean etc) and I only really use lights for inside wrecks or small caves, filming something under an overhang where the natural light is insufficient, sometimes for macro and the occasional night dive.
I found the L&M lights integrated so nicely with the housing that it would be no chore to have the lights fitted on the offchance that I need them. The lights that seemed to be readily available for reviewing on the Gates housing (at least in the UK) seemed to add quite a bit of bulk and drag and I felt I would probably end up not taking them on dives for this reason.
On the downside for the L&M I had to buy an external monitor which adds some bulk to the top of the housing (and some cost to the package) whereas on the Gates I could have viewed the cameras screen through the rear window. However, with the L&M I also have access to the viewfinder if the monitor packs up (not sure how this works with the Amphibico monitor back). I also, in many ways, like the idea of the manual controls on the Gates (having previosuly used an Ikelite housing) but I felt there was sufficient redundancy and security on the L&M so I didn't see this as a major down side.
Did I make the right choice? I hope so, at least for what I want to do. I've only had a chance to take the camera on one dive (freshwater) to try out the balance etc but I'm looking forward to getting 24+ dives in with it in the Red Sea in July
I hope this helps if only in giving you some ideas on the questions you might want to ask