How to handle dislike of/lack-of-interest in sub-specialty of research area
How does one handle this sort of situation? Is it appropriate to bring up my concerns with my adviser? 


YES. That is exactly how one handles this sort of situation. 

Try something like the following:


  I knew coming in that I'd be working on A, and I thought I'd enjoy it. But after a semester, I'm feeling.... How do you suggest I move forward?


and see where that gets you. 


  Should I wait until I've published a first-author paper in this sub-specialty first, so that I can veritably say that I have definitely given it a shot? 


If you believe you've given it a fair shot, there's no reason to wait to voice these concerns (in a professional manner). There's no "milestone" at which point you can say "I definitely don't enjoy this area" - there will always be more things to try. The reason to speak to your advisor is that he may be able to advise you on what to try next.