I would think that it would be possible for a thing called 'mansex' to exist, although I wouldn't know if that term could really come through without having some sort of baggage with it. Bi-sexual would be about the same thing, I would imagine.
As for the inclination in sexuality and sexual preferences, we may find that mental/hormonic structures rule the day--that is, call the shots, show us what we are. In the act itself, social pressures tend to determine what will be admitted to or not.
Therefore, the somewhat female-brained male may very well find the male body one which that person's eros can attach to as equally (or near so) as it can attach to the female body. I would say, holding any value of PC terms aside, that bi-sexual defines that state well enough.
However, I do agree that all that 'socially defined baggage' should be thrown out the window so that things would lighten up.
As for the Japan scene and that psychobabel, things are different from in the states, but it is stll there somewhat. The media has had a part in breaking down some of it to the level of acceptance.