Using Mark Levinson No. 380 preamp output simultaneously

Why would you do this?

n80"Why would you do this?"

It would be required, necessary, and vital to proper Music Reproduction System biamplification.

My question was not rhetorical. I'm new at this and still don't understand.

Please explain bi-amping in this context. 

n80"Please explain bi-amping in this context."

Biamplification requires the installation, implementation, and use of two distinct, separate, individual stereo amplIfiers or alternatively the use of four active stages of amplification that could be achieved with the use of multiple monophonic amplifiers or combination of such amplifiers with stereo amplifiers and in such implementations it could very likely be necessary, required, or mandatory to have two pairs of stereo outputs from the preamplifier used in the Music Reproduction System.

Why would you do this?

Some subwoofers require a line level signal from the preamp.