Ruler of the 6th in the 6th. This shows us that the 6th House will be an important theme in the persons life, as this is always the case when the Ruler of the House resides in the House.
Ruler of the 6th in the 7th would be someone who would serve his partner. Ruler of the 7th n the 6th would look to his partner to serve him.
Ruler of the 6th in the 8th would serve in a deep 8th House way such as a psychologist, a sex therapist, a detective or an FBI Profiler. Ruler of the 8th in the 6th would bring his deep understanding of taboos emotions and sexuality in to his service.Actually, in reality, these two would look the same. This seems to happen with the 6th House.
Ruler of the 6th in the 9th. This person would serve using 9th House tools such as religion,spirituality, long distance travel or Astrology. Ruler of the 9th in the 6th. This person would take his understanding of the 9th House and put it to use in practical service. This could be a pastor. These look very much the same, too.
Ruler of the 6th in the 10th would take his need to serve and would do it in a career or for the greater society, in some way. Ruler of the 10th in the 6th. This person would take his understanding of careers and society and use it in a practical service way such as a Career Counselor or a mentor to help people start new businesses. These look quite similar, too.
Ruler of the 6th in the 11. This person would do service in a group or charity organization. Ruler of the 11th in the 6th. This person would bring his experience with groups in to doing practical real world service.These look similar, as well.
Ruler of the 6th in the 12th. There may be loss with health or jobs. Ruler of the 12th in the 6th. This person may bring mystical or spiritual leanings in a practical way, to people.