What I'm thinking of doing is this
1) Members would select whether they played males, females, neuters/nullos, and 'others' (intersexed, transgendered, etc).
2) Within each of these categories members would select whether they played switches, dominants, submissives, neither, and from the given sexuality list.
An alternate step would be to add a third dimension (so someone could specify they only dominate when playing as a homosexual female and only submits when playing as a heterosexual male - whatever). That may make things more complex than is easily tolerated, however.