I am working as CMM/CMMI consultant and find that six sigma may complement CMMI level 4 and level 5
implementations. Would you agree?
I think you are on the right track. Six Sigma is a good complement to the CMM. Its analyses are fundamental to Levels 4 and 5.
I have been involved with software development since 1992, and I think where most software quality groups fail is in their absolute focus on bugs. While certainly important, they neglect the timeliness of release (the service component). In Six Sigma, we specifically focus attention on the three main parameters of service, quality and cost, and apply our tools and techniques to optimize each. Particularly when bugs are an infrequent occurrence, a lack of focus on service and cost can be just as detrimental to the business.
Learn more about the Lean Six Sigma principles and tools for process excellence in Six Sigma Demystified (2011, McGraw-Hill) by Paul Keller, in his online Lean Six Sigma DMAIC short course ($249), or his online Green Belt certification course ($499).