I answered a similar question like this a couple of days ago. Here's the answer which would apply to your question:
If you are gay, then you are stating that your attraction is to people who: shaves and maintains a mustache/beard, chiseled face, no breasts (but a very nice set of pecs), is brewing with testosterone in his blood, acts "manly", enjoys his male organs to the fullest extent, etc.
Let's make it easier; if you have an attraction towards people who look and act like a young Harrison Ford, Colin Farrell or Robert Deniro, then yeah, I would have to say your sexual orientation is definitely more homosexual.
However, you stated your attraction is to "passable feminine trannys" (which, btw, please refer to us as Trans Woman/Girls/Females as that term is often derogatory).
For example, girls such as:
http://www.youtube.com/watch?v=OaSr2Da_d…
http://ai.eecs.umich.edu/people/conway/T…
Your attraction is to that of a female: the soft skin, absence of masculine features (such as a mustache, beard, physical build, etc.), the feminine attitude, etc. That fact alone makes you straight.
However, not all of my trans sisters would agree on this statement.
I consider a male such as yourself straight because us girls don't walk around displaying our "feminine boy-parts" out to the public. We don't walk around stating what is between our legs or what was between our legs. Everything about our bodies (our mind, spirit, body) is female, except that ONE part. Gender is not found between our legs but what is in our heart and our mind (it's a biological birth defect, anyone who attests, go do your research please before spewing out your ignorance!).
Your attraction lies on the basis that what you see in public is what attracts you. Last I checked, walking around nude in public is illegal, so therefore it may often be hard to spot trans women out from the general public. Unless your true intention was to find some way of experiencing a male penis during your intimate time without feeling guilty that you might be "gay" by experiencing it with another man, I would then state you probably are bi or borderlining gay. Though you state your attraction does not lie there, therefore, you're straight.
I have dated and maintained long term relationships with men who did not find out about my transsexual status until a couple of months into serious dating (and keep in mind, I am a pre-op--meaning I have not yet had SRS). Many of them shocked as they had absolutely no clue. However, many of them stayed and treated me like they would any girl they dated. I was explained that from their point of view, they would never have thought of the idea of maintaining a relationship with a trans girl before, but because everything I embody is female, they refuse to think otherwise.
There exists a huge misconception that trans women look like a "hairy man wearing a dress", are insane, or are all prostitutes.
There are many trans women who will blow those stereotypes away, and I am one of them. I consider myself very attractive, passable, smart, and successful. I graduated college and am maintaining a very successful career. Basically, a young normal girl living with a birth defect.
I don't understand why people choose to use labels in order to define a person. Gay, straight, bi--in the world of love, those labels simply fail to exist.
Ps. I could only hope that you are not using us trans girls as a sexual object and treating us like the women we are. You can absolutely date us and maintain a loving relationship (if that's something you are looking and ready for). Some girls are passable, some are not, some have problems, some don't--basically, we are just like any other girl you have seen or known. We simply have a spirit which has survived great obstacles and found a way to find peace with ourselves, and our bodies.
I'll simply state that if we are to only remain as a sexual fetish for you, then you'd be considered a "great assh*le" in my book.
