I've been wanting to try DoL+ for a while but I don't think it's possible at the moment to use them both. From my understanding reading the mod discord, both Firemod and DoL+ have many changes to the code and aren't available even in Modloaders for the game. I admit I don't know a thing about making mods and don't have specifics on why a merge hasn't been figured out yet, but it's a shame.
I see Firemod as just about mandatory because of how much it adds to sex scenes and it blows my mind that Vrelnir hasn't reached out to somehow include it to replace those ugly vanilla x-rays after all this time.