- Genesis - when something is new and unknown (Agile),
- Utility - when something is a cost of doing business (developed by 6-sigma), and
- Transitional, which is, well, transitional and sits between Genesis and Utility (Lean).
'6-sigma' is considered to be a dinosaur. A methodology of the past put in a row with waterfall.
Sit down and watch what will happen, because this is one of the most amazing things I have seen.
Agile will be bent, then bent again, and then twisted. The team will proudly introduce the most important 6-sigma principle (hypothesis->data->decision->action) while loudly declaring they are still agile.
There is one thing to remember - make sure the component is small, because only then will you have reasonable confidence that your team and the task are consistent. The bigger component you define, the bigger are chances that some part of it is truly agile and requires experiments.
Therefore you should be focused on one thing - how to cut your system/organization into proper and consistent components. You do not need to worry about bi-modal or three modal approach. This will appear spontaneously in your organization if you have proper components (and keep agile/6-sigma consultants away).
Remeber: Your task is to cut out proper components.