I cannot say if 8 modes are possible, but 6 are. I dont have your exact hardware, but i think you should be able to make progress with my settings as a starting point. When I get some time, I will post a video of my method for setting up channel mixing for using flight modes with any radio. Send me a reminder if I dont post in the next week or so.
Here are my settings for the Turnigy TGY-i6. These will give you six (6) flight modes using SwC and SwD
Firmware 1.1 9-Jan-2015
Endpoints Ch5 67% 50%
Aux. Channel 5 Source SwC
Aux. Channel 6 Source SwD
Mix is ON
Pos. mix 4%
Neg. mix 50%
I configured my flight modes as follows:
ArduCopter Flight Modes
The 3 main modes I use are PosHold for flying with the kids, Auto for running missions, and RTL when it's time to land the bird. With a flip of the 2 position switch, I can go from PosHold to AutoTune, from Auto I can initiate RTL, and from RTL I can pause by going to PosHold.