The SX fretless is the low B flop champion of the world, that I'm aware of, and I've never figured it out either. Thus, I do the exact same thing, ala Steve Digiorgio tuning on my SX fretless. Try
www.stevedigiorgio.com/equipment to check out what he uses. ESP's generally use EMG pickups last to my knowledge (I could be way off, but quite a bit of ESP's substance is in the pickups), so you may want to swap the pups with the EMGs. That and technique should get you roughly close to Steve's sound.
Also, the SX fretless five string tends to work great with tenor tuning. I probably need not tell you this, but if you're playing with bands who tune to double-drop Z, it's still possible to stand out with the bass in that tuning, though it'll take creativity. FWIW, I'm actually working on a solo project in the death metal vein using that aformentioned SX to record all "fretless guitar" and bass parts.