I stay away from Flats personally on a warwick bass. They sound deep to me even with everything flat etc.
So i like more brightness on the string for warwick.
I only have a 4 string crovette but i used stainless steel strings like Rotosound or DR LoRider. Could try some Nickel string.
Fender Jazz Bass Club: #168, Fender Precision Bass
ACG J Type 5 Bass, Ashbury Acoustic Bass