There's nothing inherently female about the Howling Banshees or the aspect of Khain they represent, it's just that the Phoenix Lord for their aspect is female, and tends to have a higher percentage of female members. This doesn't mean that all armor is designed for females and that males just have to adjust, there are armor versions for both genders, same thing for female warriors joining other male predominant aspects. And as for the models, I don't know why there aren't any male models, you'd have to ask GW on that, but I always figured that this was simply because the gender ratio might be lower than 10% male, so in a squad of 10 it would be a rare occurrence.
