How to fix hole in shower wall

Hoping someone has a brilliant idea. Shower in IP developed a leak behind wall. Turned out to be the breeching piece behind the taps. Plumber has fixed but now a sizable hole in the wall (i'd post pics but wife's out with camera).

The hole is 400mm x 300 mm (4 tiles) and taps are in middle of hole. Taps are fixed to timber noggin behind. I wave a wall stud down one side but nowhere else to fix the board to.
Firstly, can I use standard fibre cement sheet or do I need the aqua stuff?
Secondly, I can nail the villaboard to the wall stud and thinking of using an offcut of villaboard to sit behind sheet using liquid nails.
Thirdly, after I've tidyed up the hole and fitted the sheet, how do I fill the gaps around the sheet to waterproof it prior to tiling?

Any advice is appreciated.

Project 1080

The project: 10 IPs in 80 mths.
This may not be much help to you, but this pretty much describes out situation in our PPOR several years ago. I cannot remember the details, but our insurance covered us and would have paid for the wall that the taps were on to be resheeted and retiled. Because the tiles could not be matched, they paid extra to tile the whole shower stall.

We told them that we would rather take the equivalent in cash because we had planned to rip the "lovely" 1970's brown patterned tiles out within a year or two and they gave us a cheque to bank and put towards our bathroom reno.

It cost us an excess, but it also paid out for things in our linen cupboard behind the wall which suffered water damage.

Perhaps check whether insurance covers this, and if so, you would possibly be better advised to resheet the whole wall and retile the whole wall rather than risk water getting through your repair.
crap at writing but i will try??
remove tiles, i tile width away from the hole,
the wall surface should be villaboard, 6mm , cut the hole square with a grinder, or take your time with a stanly knife by continuing scoring the surface , through all 6mm depth, dont cut yourself?
when the larger square hole is done, using chipboard screws, 25mm length, screw a piece of "pine" to the back of the sheet by screwing through the front of the villaboard, do this on two sides, ie top right and bottom left corners, hold the timber firm with left hand and drive screw through with right,

then cut piece of new sheeting size of hole and screw in place , top right and bottom left, allowing the screws to grab the pine and pulling the new peice in tight, then plaster square edges, "joints" .

then wet seal all exposed surfaces, twice, allow dry 24hrs, then replace the tiles, good luck , PM me if you have trouble, and i will give you a phone number to call me on , good luck cheers, ;)
Thanks Craigb,
The process is similar to what I do for patching Gyprock holes. I have a couple of other questions on the detail so I've PM'd you.

Project 1080.

The Project: 10 IPs in 80 mths.