How Do You Implement a Uniform Sales Compensation Plan?

The Situation
You’ve just been hired as the sales leader for a six-person sales team. One of the issues that the owner of this small business shared with you during the interview process is that each of the six people is on a different sales compensation plan. Some are paid salary-only. Others are paid a mix of salary and commission, but the salary and commission rates are not consistent.
The business owner has tasked you with developing a single, sales compensation plan for all of the salespeople. Yet, he is also concerned that some of them will leave due to the change.
Your Challenge
How do you implement a uniform sales compensation plan? How do you communicate the plan to the team?