I think that it can be fun to have another woman involved in your play. Either as an equal femdom lady or as a female slave. A female slave is slightly higher on the food chain than a male slave. The male slave must serve both his owner and the female slave and please both. This is quite amusing indeed.
Sexually it can be fun to have a female slave ride your man from behind whilst you ride her also from behind or whilst your whip her to set the pace.