When I got my 604, to get the tone closest to what I wanted, I fitted flats, played passive on neck pickup.
Now I've a BB to satisfy that need, I'm able to be a bit more relaxed with the TRBX, letting it find the noises it wants to make.
I can't now remember where I read this advice but it's been good: with the TRBX 500/600 3 band eq, boost the mids and cut both the highs and lows. I've found that works especially well with the pickup blend 50/50.
However the Chromes are now wrong for this sound (too bassy, and their husky quality is fighting the tighter focus the eq is trying to create) so I'll try a 45-105 set of Rotosounds next, either Roto Bass RB45 or Swing Bass RS66.