Mike,
What I understand is.. U just want to give 10% discount to the customer base on variant combination.
If that is then you can achieve this by creating one more characteristics. Ex - (CH_VAR_SURCHRG)
With the mapping of variant price table (SDCOM) and field name (VKOND) in additional data TAB of cstics.
Now you have to create some object dependency (Procedure) to achieve Variant key for the combination of two Cstics. (CH_A = X & CH_B = Y then CH_VAR_SURCHRG = XY)
Create one condition type by coping the standard variant condition type (VA00) and make some changes to make it available for discount.
Keep reference image settings in condition type.
Hope above English is giving some idea to you. Now process further and make required configuration in pricing procedure and make condition record for the XY combination with 10% discount.
You will achieve your requirement.