Mono block Preamp

Typically a two box solution will be separating the power supply and amplifier section. Since a preamp is amplifying at such low levels I think designers felt they got more bang for the buck by getting the high voltage stuff away from the low voltage stuff.

Esoteric makes one-dual power cords need

Seems like I vaguely remember an early Sutherland, 5000 maybe?

Most of the advantage of going monobloc is to reduces cross-talk (channel separation).  Monobloc is of more advantage when there are big voltages running around, like in a power amp.

The volume control requirement in a pre-amp is an inconvenience that will put of many aspirants.

Monobloc phono amps make some sense.