First, you're welcome! Second, I have my answer regarding your question about voice in employee involvement. This is what I discuss in my leadership development programs with senior leadership and C-level executives from client organizations. However, I will not answer your question. Not because I want to make it difficult for you but because I want your dissertation to be a rich and invigorating experience. You have chosen a topic that is extremely powerful and almost entirely separate from most run-of-the-mill leadership dissertation topics.
Third, regardless of the leadership style context in which Voice is analyzed, the outcome is always the same. The only time it varies is when applied in the context of management as opposed to leadership.
Regarding researching in a 'live organization,' my suggestion, given your choice of topic, is to select one that has existed for at least 25-30 years. It is only in sustainable organizations that Voice is truly visible as a core part of ordinary business culture!
Once again, good luck and have FUN!