Hm yeh well I guess I do split frequencies but I like to do it with the layering. Like I make a VST synth thats plays something cool, then if it lacks power in the highs let's say. Then I just copy that track with the synth and modify it to do something else to fit that spot kinda. But I think it gets kind of messy if I leave the lows of the new sound so I HP it and LP the other.
One thing I think is hard with freq splitting is to get it to sound like one solid sound again, sometimes it works out. sometimes it does not. And then I gt do something else