I always figured that's why people make sockpuppet accounts there.
I can say that a lot of people suggest you let your two partners work that out between themselves (with your input of course if that is how you roll and all). That is if you don't want your husband to be #1 in decision making, or your other partner for that matter.
Might want to sit down with "Opening up" with both of them at some point and go through the stuff about how you want to practice other relationships including the bit about BDSM. (or do some group emails if that's more comfortable). I am sure it will bring up some interesting conversation, and you can really find where there might be problems, or that they both are on the same page with things and there won't be any overlap that is an issue.
Happiness will never come to those who fail to appreciate what they already have.