Hi pgastone.
I edited my previous post to clarify that I was referring to the tube buffer with my second paragraph. Regarding the buffer, I'm using it with 6H30PI tubes. They sound neutral, doing nothing other than their job, which is to provide a high input impedance facing the Tortuga controller and a very low output impedance facing the power amp. Their job is not to add a euphonic "tube" sound to the system, but just to optimize components impedance interaction. Colorations, tube or solid state, over time show themselves to be deviations from realism.
I initially compared the Tortuga LDRxB against my Audio Research REF3. The Tortuga bettered the REF3 in every respect. Since then, I compared the Tortuga with a variety of preamps, some costing five figures. None could equal it.
I'm using the VonSchweikert VR100XS speaker system. Mine have the Ultra upgrade with MasterBuilt Ultra internal wiring and internal crossover component optimization voiced by Albert. I also use MasterBuilt Ultra cabling. My DAC is the Lampizator Pacific. By the way, it likes the Tortuga input impedance set to between 85 and 91 kohms per phase. I vary the input impedance (using the remote) depending on the recording characteristics.
Regards,
Robert