I find no legitimate reason why either partner shouldn't be sexually satisfied, even if one is asexual or both are differently preferenced from each other. Also I'm adamantly against people raping their own psyches with a sexuality that doesn't come naturally for them just to satisfy their partner's sexual preferences.
So given monogamy as an absolute, I wouldn't even consider such a relationship without being fully sexually compatible or at least enough so as to reduce to a minimum any sexual frustrations; but given an open relationship, which you do not have within these parameters, as viable option, I see no justifiable reason why sexual preferences should interfere with intimacy otherwise expressed and enjoyed and I feel that we rob ourselves for no good reason of perfectly satisfying relationships when we insist otherwise.
Saying that companionship is "nothing more than" friendship is stupid. Marriage, partnership, coupling by any name is, or certainly ought to be, first and foremost, companionship. The only people I ever considered best friend were my partners.