Your heroes are quite dark, with a tendancy to violence (sometimes sexual violence) and domination e.g. lysander! Do you find it hard to keep a balance so they are still worthy of the heroine? 
That’s a great question.  I think you are very perceptive to observe that heroes really do need to be worthy of heroines, especially when said heroes aren’t falling all over themselves writing poetry and delivering flowers.
You are also correct that in my novels, my primary heroes tend to be dark and strong.  My secondary leads can vary, such as Robert of Stonehollow or even Jaxx of Interplanetary Slave .  But I think it is intriguing and of literary value to write darkly.  It’s no secret that much of our entertainment throughout history in all forms is dark, often far moreso than what I write.  
Obviously, a line separates the heroes from the villains, even if both are prone to violence and domination.  An example comes to mind in Pirate Barbarian in which we have two very violent and authoritarian men who feel they are right for Jolene.  Yet Jolene’s fiancé, Raul, is clearly a scoundrel and the equally ferocious, Kai, is clearly a champion.  What’s the difference?
Here are a few thoughts that come to mind:
Devotion.  To craft a worthy hero, I think the hero should have a weakness for the heroine.   If the hero adores her (even if he doesn’t admit it), it is easier for the reader to feel he is worthy despite his dark tendencies.  When push comes to shove, my heroes, bad boys or not, have some underlying devotion to the heroine.  We see this in characters like Lysander, Arystan of Warlord and Lucas of Stonehollow .  
Follow-through.  If a hero says he will do something, he does it.  This preserves the heroine's respect (and the reader's).  This is apparent in leads such as Lysander and Xane of Master of the Galaxy .  
Strength of Character.  Having a backbone is important since my novels aren’t about limp fish.  Stories about weak and conflicted heroes are fine but that isn’t the tone one expects in my books.  My heroines won’t usually find the heroes having nervous breakdowns, although I admit they may have moments of self-doubt.   And because my heroines (Arcada, Abigalia, Jolene and Sara to name a few) tend to be mentally and physically tough, this is necessary to keep the equilibrium.
Likeability.  On some level, we love these heroes, even when they are wicked like Lysander and Yoshiro or harsh like Terenth of Interplanetary Slave .  They generally possess some good humor, have a sympathetic background or are just too darn sexy not to fall all over.
Finally, as to whether I as a writer find it difficult to keep the balance, to be honest I don’t.  My characters emerge naturally and without much of a struggle.  I don’t tinker with their personality traits to make sure they stay consistently likeable and heroic.  I think it helps that I write sequentially, letting my characters grow on their own through dialogue and interaction and they often surprise me with how they turn out.  In other words, I don’t have a “master plan” before I write about the “masters” themselves.

Thanks for the enquiry!