From what I have seen in the poly community, it is one of the more open and accepting groups. I think talk of transgender or transsexual may raise a few eyebrows, but poly people tend not to be too judgemental about who another person is with (as long as it is ethical).
I think the poly community tries to be open minded because acceptance of a lot of stuff we believe in usually comes from being open minded. In contract, swingers tend to be less accepting of gay men and transgender/transsexual people.
So I think you will find acceptance in the poly community. But for personal preference for a relationship? I am not sure. Personally, I tend to be attracted to a person overall. So looks, personality, ethics, intelligence, hobbies, etc all affect how attracted I am to that person. So I could be atracted to transsexual/transgender people. But since I have never done something like that before, I am partly guessing.