Usually any impedance over 10k is considered high and acceptable by most preamps. The more sensitive preamps will start to roll off high frequencies as the amplifier impedance drops or the volume control is changed.This statement is not correct! For example ARC recommends the amplifier input impedance be no lower than 30K. In any event, if the preamp does not like the input impedance because its too low, bass will suffer at any setting of the volume control.
This is moot if the Parasound stays and I agree with others that it is the better amp over a Rotel! It has a high enough input impedance that most tube preamps will be fine with it. There are balanced line tube preamps; we make some, so does BAT, ARC and others.