I suspected there was far more to the story than your first post indicated. There you asked if we concurred with your decision. Now it seems that you've already made that decision, and are asking about how to proceed. I am assuming that you already have kept your senior pastor informed, and have his full support. If not, take it to him now, before proceeding, even if you have full authority. Zach's already given you some good advice, and I would like to add a bit.
Without knowing the issues involved, of course, we can't be very specific. Still, some basic principles apply. Some thoughts:
1. The way you handle this can be the biggest deciding factor affecting this brother's spiritual well being. Exhibit Christ like love, concern, forgiveness and grace. If possible, have your senior pastor with you as you meet with him about his stepping down. If not your pastor, then another trusted, mature leader in your music ministry. You'll want a witness as to what is said, and how this is handled. Make sure this person is up to speed on the situation before such a meeting.
2. When meeting with the person being asked to step down, be genuinely as uplifting and encouraging as you can possibly can be. Be specific in whatever praise you can give. Thank him for the whatever you can thank him for.
3. Be as specific as you can possibly be in describing the problem. First, review your past meetings with him about it, what was said and what was expected. Then review the moments of progress and lack of progress. Don't settle for nebulous "lack of chemistry" charges. He'll never be able to work on those. Give him specific things on which he can work.
4. Be clear about whether he is to merely step down for a while, or if his "suspension" is permanent. Don't leave him guessing.
5. If the suspension is not permanent, be very clear on any conditions that must be made in order for him to return. This is true whether the issue is skill, trustworthiness, commitment, attitude, punctually, etc.
6. Especially note any required time frame for a possible return. If you're thinking 6 months or a year, make certain he doesn't have the impression that he'll be back in 3 weeks.
7. Before the meeting closes, allow him to respond. Listen carefully to what he says, and what he doesn't say. Don't be too quick to interject.
8. In closing the meeting, pray, genuinely thanking God for this person and his gifts, asking God to continue to bless him and help him grow in his discipleship and usefulness in the kingdom. Ask the Lord to use all of you to help people know Christ more deeply and follow him more closely. Mean it! Then offer a brotherly handshake or hug, and be done.
Two weeks after this meeting, let him know in person, if possible, that you haven't forgotten your commitment to pray for him, and that you wish him only God's greatest blessings. Do it again in three months. Remember: your goal here is to build up not only the team, but it's individual members as well, even one who has been asked to step down,.
cotten