I have a pair of Tortuga controllers in my bi amplified system. I use an LDRxB as the main controller and an LDR1B ahead of the bass amp to level match with the mid/tweeter amp. The system doesn't have a buffer, so the adjustable input impedance is important to getting the most "umph" out of the system as possible.
That said, I've found that another important use for the variable input impedance control is to get the most from your source component (a Lampizator Golden Gate DAC being replaced with a now being traded in for the Pacific DAC). I found a good approach to finding the input sweet spot is to start with coarse steps such as 10k or 20k at a time. Once you've isolated a range on which to focus, set the steps to around 2k at a time. Note that I use the balanced variants of the Tortugas, so the net + to - impedance values are double the indicated values.
For my Golden Gate, I ended up with 5 settings of 83, 85, 88, 91, 93k. Each step had its own sonic nuances with different recordings sounding best at different impedance settings. Using the lower settings, the top end opened up, benefitting vintage recordings. For most recordings, 93k was very well focused and would tame hardness in some lesser quality recordings. The sweet spot was usually 91k, though 88k generated a synergy with the bass amp and helped bass shy recordings. Of course since my system doesn't include any active components between the source and the amplifiers, the differing loads presented by the bass versus M/T amplifiers factors into the final sound.
After having lived with the capability of fine tuning input impedances and being able to switch between them with the remote, I've come to appreciate the value of that level of control and its importance to getting the most from my system. That plus the absolute phase inversion option (again controlled from the remote) are features that I would not want to be without.
By the way, both of my Tortugas are back in Morten's hands as I'm getting the V25 and OLED upgrades. I'm sure looking forward to getting them back in my system.