Most pre amps with a balanced input and output will have impedance specs simular to the ones mentioned. In a balanced output stage the designer will put protection resistors on the outputs and the value doubles because now ther is two of them in a balanced configuration.
The input and outputs being balanced will quite often double the impedance specs but that does not mean that the input stage did not convert the signal to single ended. The signal then gets processed just like any other pre amp and then gets converted back to differental in the output stage. A fully balanced design has a four gang volume control vs a dual unit for a single ended design. There must be twice the gain stages in the fully balanced design. I hope this clears up some confusion. Chris
The input and outputs being balanced will quite often double the impedance specs but that does not mean that the input stage did not convert the signal to single ended. The signal then gets processed just like any other pre amp and then gets converted back to differental in the output stage. A fully balanced design has a four gang volume control vs a dual unit for a single ended design. There must be twice the gain stages in the fully balanced design. I hope this clears up some confusion. Chris