We've had many females, and males together at the same time without issue.
I had Emma and Sally, and they grew to be like two sisters (who loved one another).
Growing up we often had two female Goldens, but rarely two female JRT's. We had two female Wolfies at the same time. We also had more than one male at a time. I now have Oliver and Henry.
I think the major contributing factors are first whether or not a male is intact with another intact male. Secondly with females, it may come down to the breed, but for the most part, again, that can work too, obviously.
The most important thing is how they are introduced and how the "first" dog is treated.
Kristen's recent history of Fostering is case in point.
Acceptance of a new member of the family is all in the way we handle the introductions and how we establish the "rules" moving forward. I honestly don't think gender plays a huge role in this in most instances.