Details for bi-amping

You do not need two preamps. You can use Y connectors from a single set of outputs, that is what I did when I biamped. Use good quality Ys. It is not clear if you are using 2 matched pairs of amps or 4 different ones. In the first case you will need level controls for the pair of amps that is more sensitive, ie plays louder as a given preamp setting, so you can lower their output. Using mismached amps would require 3 level controls at least and be quite complicated to set up.

Thanks Stan for your quick reply. My ignorance needs a lot of clarification. I intend to use two matched pairs of monos. As you said in this case I will need a level control for the more sensitive pair. Saying "sensitive" do you mean more powerful? If yes, how could I make this setup? Obviously the level control of the single Pre-amp is not useful for that because it would attenuate (lower) the output volume of all the four monoblocks.

Parts Express carries the Harrison Labs fixed inline attenuators in 3, 6 and 12 dB versions. Right now, your guess is as good as mine which you might require but you only need them for the amp with higher gain.

My experience would advise to stay away from variable, potentiometer based units.

Passive volume control attenuators, such as Goldpoint, can be too rough for fine tuning biamping configurations and have fixed input impedance. Which brings up the other consideration of parallel amp impedance getting reduced and whether the preamp can handle that. Usually not a problem for solid state preamps.

Fair warning: Many biamping experiments, passive or active, end in failure because it's far more complicated than most people anticipate or are prepared to understand.