I'm also in (an) open relationship/s. My female live-in partner is not explicitly vanilla, but not a sub by any means. My male partner is a fellow Dom. Our solution is for him to have his playmate on the side, who matches his particular kinks very well (and is generally a really good guy, I also get along with him well) and for me to have regular play sessions with a close friend of mine with whom I have a sexual friendship- who is in an open relationship as well. Much less headbutting at home with two happy Doms.