The Rocksong neck is a muddy pickup, easy as that.
I think it's only the Invader neck which has that capacitor. It just acts as a coupling cap. I don't know much about using them with pickups though, cause it's only extreme cases where it is needed.
Perhaps give "Artie's Mod" a bash. Basically it's a capacitor and resistor in parallel, put in series between the coils. I personally am not a fan of this as I like to have pickups sounding good without anything else in the circuit, but with a pickup like the rocksong, I can understand why someone would use it.
Here's another idea, why not replace the tone control with a bass control?
