Hi! Thank you brother!! I am pretty sure you will get a great fretless tone from your bass, just experiment a few more times.
What I suggest first is that you put the strings as close to the fretboard as possible, quite low action. But still so, that the strings will ring clear when playing open strings with medium touch, no buzz or rattling. For fretless I use mostly Nickel strings 45-65-85-105 R.Cocco or Elixir. For recording R.Cocco because there is more edge without the coating. R.Cocco also fits the Alembic basses I have (they need long scale + strings)
For legato try to play on the fretboard with your right hand, you will get a full round growling sound. I might also play with the soft side of my left hand finger for some legato things?
Well, no amp is actually really flat ever, but I usually keep the knobs on the amp I have straight. I do most of the adjusting with the bass and with the fingers.
Ps. I will be at NAMM in January are you going to be there?
Best Regards,
Jan-Olof Strandberg
www.jostrandberg.com