You can't use both!
Your diablo will come with a standard program with the timing advanced. The amount of timing advance depends on rpms that the motor is running. As rpms climb, the amount of timing is increased. Stock, the timing is set at 10. The diablo will probably max you out at 14 or 13.5 or something like that.
The adjustments that you can make are only a small fraction. By 10%, I believe they mean 10% of the difference between 10 and 14 degrees of advance. You will never be able to get the diablo to advance to 16 w/o returning it back to the factory and having a different program put on it.
The adjustments that the diablo allow you to make are soo small that it amounts to not much more than a gimmick.
If you advance your diablo by 10% and your tuner is set for 14 degrees, then your advance will now be 14.4%....that's it.