The Opposing Democracy would work for the Romulans, the Cardassians would be the Military Dictatorship, the Klingons being the Space Samurais.
That leaves the Ferengi open as basically the MegaCorp enemies of Trek. Basically take something like Weyland Yutani and make them a Trek enemy/presence. They sell routes for shipping lanes, to anyone who has the money (including Pirates), they sell weapons to anyone who can afford them (thus meaning if both sides can afford, the Ferengi will keep wars going for centuries as it cuts them a profit and neither side may find out what's happening), when you make a move on them they respond by taking control of a major resource trading network you rely on so you HAVE to back off.
Basically, have their power come from everything EXCEPT military dominance.