I used to have similar problems, as my favoured bass sound had the EQ set in the old V formation with heavily boosted bass and treble. The G and D strings disappeared above about the 5th fret. I decided to start again from scratch with level EQ, then adjust slowly to get an even sound across all the strings. I put the EQ flat, and the problem was solved immediately - so I didn't bother with any more fiddling. Maybe that would be a good start for you - turn the filters off, set the EQ flat and maybe that will give you what you want.