Maple neck? Boy, you've got bright tone just DYING to get out of that bass. And regular flats aren't doing it, eh?
At least two companies (prob. more) make a nylon-coated flatwound string. They're black, and you'd swear they were plastic if you'd never seen them before or didn't know what you were looking at. These are some of the mellowest, thumpiest strings I've heard (which is why I don't use them), but they may work very well for what you're describing. Worth a shot - hope you find what you're looking for!
__________________
THUS ENDETH THIS THREAD. <-- So sayeth Fretlessman71, a.k.a. "Thread Killer"
Yeah, they don't have the same tension as other strings - they're more like a big classical guitar string. But the sound is very unique; you may prefer them after you get used to them. Otherwise, a set like this might do you well: http://www.juststrings.com/ghs-3060.html
__________________
THUS ENDETH THIS THREAD. <-- So sayeth Fretlessman71, a.k.a. "Thread Killer"