It sounds like A is on the same page as you guys, and Indigo sounds like he's OK with A. That makes everything so much better, when your BF knows and accepts the importance of your husband and your marriage, and your husband and BF can laugh together at their first meeting.
I remember having dinner with L and D the first time, and how D and I talked a lot about his sculpture and my writing. L was with us but content to let the guys find common ground. (*sigh*)
But L and D have had an open marriage for a decade or so. It sounds like you, Indigo, and A had a good experience the first time and that's what you build on! It's great.