I posted this update on the reprap forum this morning but as many reading this may not use that forum I'll copy it here in the hope someone may be able to contribute:
OK some success, I'll post what I've got in the hope that someone else can fill in the blanks. I have now gone over to the dark side and used Repetier firmware which is not ideal as it works strangely with Pronterface. But the aim is to have a stand-alone machine that doesn't need a computer tethered to it so it really doesn't matter as long as it works. With Repetier the panel works with all the lights and the rotary switch selecting etc. and the LCD works of course.
On the back of the Viki there are two 6-pin headers, one for the I2C and the other for the SD card. My Viki came with two 6-pin to 6 individual pin fly leads so I plugged one into each header with the 6-pin blocks at the Viki end thus:
You can see I lined up the red wire in each onto the same corner as in the case of the left hand one (as per the photo) that is +5volts.
The Azteeg X3 has lots of places to attach the other end of these leads so first up I worked on the I2C as I knew this ran the LCD display and suspected it did a few other things too. It turns out that all the indicator lights, the selector switch and the LCD all run on the I2C bus. the only things that don't are the pause/run switch below the rotary switch, and the SD card stuff.
So taking the lead that runs from the left hand 6-pin header on the Viki (the one that has +5v on the corner pin) this goes to Exp3 header on the Azteeg X3. This connects as per this photo below, and if your lead matches mine would be like this:
Green @ @ Blue
Yellow @ @ Red
White @ @ Black
The position of the Yellow and White leads determines which way the rotary encoder works so if you want your encoder to go down the menu with a clock-wise rotation then do it the way I did.
Less obvious is the SD card connections and I still haven't gotten this working, however I have made some headway with the Azteeg pinout of the ICSP header. This header has clock, data in and data out as well as a reset button plus +5v and Gnd as per this layout (looking at the header on the back of the board with the dot top left):
MISO (DO) @ @ +5v
SCK (CLK) @ @ MOSI (DI)
RESET @ @ GND
So I have connected the second lead from the Viki (the right hand one in the photo above) like this:
White @ @ NC
Green @ @ Blue
NC @ @ NC
So that leaves three wires that want digital inputs to attch to for the run/pause switch, card detect and chip select. I have tried a random selection of available pins for these and so far not had any success. These pins are probably assigned somewhere in Repetier but I haven't found the reference yet. You can connect the black wire to the reset button if you want a reset button on the viki panel but personally it is too close to the rotary encoder for my liking and easily hit by mistake.
I also think there may be a hardware link to add or remove somewhere on the Azteeg X3 to force it to look at the remote SD card as it seems odd to have two SD card slots otherwise. There is no documentation to show this of course.