Hello Dantakayama,
I'm auditioning the LDRxB. This passive controller retains the punch and power in the bass while providing transparency, air, and superb high frequency extension. As with all passives, attention to impedance and how the source and amps mate with the LDRxB matter. If your source DAC has sufficient drive and if your amps present a half decent impedance, the Tortuga is mighty impressive. It has no problem driving my Spectron monoblocks which each present 25 kohms. I don't know yet if it can handle my bi-amped system, since the net impedance of both amps drops even further. Anyone out there have experience with active buffers (tube or solid state) to ameliorate very low amp impedance?
I haven't tried other LDR passives, but given that LDRs resistance curves drift with age, the self calibration capability of the Tortuga offers several advantages. First, this means the individual LDRs will remain matched over the years with an occasional calibration. In the event you want/need to replace an LDR or if a new improved version is available in the future, the LDRs can be replaced in the field much as a tube can be pulled and replaced.
As for the remote option, I wouldn't want a controller that didn't have remote volume control. My understanding is that the hand held remote controls the volume exactly as the front knob on the preamp. With the Tortuga, you're actually sending a control signal to a microprocessor which essentially sets the LDR brightness level based on the current lookup table generated from the last self calibration. Since I use a balanced system, including the preamp, this ensures that the + and - phases of each channel remain matched for the life of the unit,
As I said, I haven't tried other LDR-based preamps. If you have a chance to compare multiple vendors' LDR passive preamps, please post your listening impressions.
Best,
Robert