Hi Shredder. What's the input impedance of your current preamp? Can you adjust it to get a perfect match for your Atlantic? I've found that after trying many settings that my Golden Gate sounds best in my system with the Tortuga's input impedance set to somewhere between 79k and 89k (per phase). I have saved settings (you can save any five values) now at 79, 82, 85, 87, and 89k. Switching values is just a couple of clicks on the remote.
Below 79k the mid/treble starts to be a bit forward, though spacious. Above 89, dynamic transients begin to be a bit tame. I've found that most of the time, I use 85k which has great width/depth to the sound stage and the bass is at it's best in terms of dynamics, frequency extension, and control. I also use different settings for problematic recordings (e.g. older/dull recordings that need some brightening or those with a transistory hardness or glare that need to be tamed).
My Tortuga has a challenging output load to drive with mid/treble amps of 100 kohm input impedance and bass amps with 25 kohm impedance. I use a second Tortuga LDR1B (one fixed balanced input) ahead of the bass amps. I have the input impedance of the LDR1B at 85 kohm per phase and the attenuation set to around 63 (where 70 is no attenuation).
Your optimum input impedance settings may differ of course, but my system is far from what would be considered to be an ideal match for a passive controller and the LDRxB fits in just fine.